DEPARTMENT OF PHYSICS IN-HOUSE SYMPOSIUM 2008

DEPARTMENT OF PHYSICS
IN-HOUSE SYMPOSIUM 2008
INDIAN INSTITUTE OF SCIENCE
BANGALORE 560012
(NOVEMBER 24-25, 2008)

FORWARD
As a periodic review of its activities, The Department of Physics has been
organizing In-House Symposium on annual basis during recent years. This one-day
symposium usually consists of oral presentations by selected faculty members and
students, and poster presentations by all those who would like to present their recent
results. This year we have 10 talks by faculty, 2 by post-doctoral fellows, 17 by the senior
students and as many as 28 posters by the rest. I hope this package would be as
reasonable representation of the ongoing research activities in the department. This event
is also particularly useful to freshers to familiarize themselves with the current research
activity in our Department in various branches of Physics.
I would like to thank Drs. Prabal Maiti, Arindam Ghosh and Banibrata
Mukhopadhyay of our Department who have shouldered the responsibility to organize
this In-House Symposium. I urge all of you to actively participate in this important
scientific activity. I hope you will all have an enjoyable and fruitful day.
Prof. Chandan Dasgupta
Chairman
November 24-25, 2008

08.55-09:00 Welcome
Chandan Dasgupta
IN-HOUSE SYMPOSIUM
DEPARTMENT OF PHYSICS
Indian Institute of Science
November 24-25, 2008
TECHNICAL PROGRAMME
(Venue: Physics Lecture Hall- I)
Day 1
(24/11/2008)
09:00-10:25 SESSION I
Chair: Vasant Natarajan
09:00-09:20 F1 Chanda J. Jog
The surprisingly flattened dark matter halo of the Andromeda
Galaxy
09:20-09:40 F2 H. R. Krishnamurthy
Novel Physics in Hetero-structures of Strongly Correlated
Materials
09:40-09:55 S1 S. Srivastava
Polymer nanocomposites near glass transition: Role of interface
09:55-10:10 S2 Naresh Babu Pendya
Observation of low temperature Persistent Photoconductivity in
flower shaped dendritic PbS structures
10:10-10:25 S3 T. Phanindra Sai
Fabrication and Electrical Characterization of Charge Transfer
Molecular Wires
10:25-11:00 TEA
11:00-12:55 SESSION II
Chair: Prabal K Maiti
11:00-11:20 F3 Chandan Dasgupta
Growing length and time scales in glass forming liquids
11:20-11:40 F4 Jaydeep Basu
Nanophotonics with Quantum Dot Arrays and Optical Near Fields

11:40-11:55 S4 S. K. Biswas
Diffuse optical tomographic non-invasive breast and brain imager
using a single laser light source
11:55-12:10 S5 Murthy O. V. S. N
High pulsed field magnetotransport and hole mobility in HgCdTe
12:10-12:25 S6 K. G Padmalekha
EMR Studies of LSMO nanoparticles dispersed in PVA
12:25-12:40 S7 Mogurampelly Santosh
Force Induced DNA Melting
12:40-12:55 S8 N. Kamaraju
Ultrafast electron dynamics and cubic optical nonlinearity of
single and double walled carbon nanotubes
12:55-14:00 LUNCH
14:00-15:30 POSTER + TEA
15:30-17:15 SESSION III
Chair: Rahul Pandit
15:30-15:50 F5 A. K. Sood
Nonequilibrium Fluctuations in Sheared Jammed States
15:50-16:10 F6 K. P. Sinha
Extended Einstein-Hilbert (E-H) action and the emergence of
Riccions as cosmic dark matter and consequent cosmic
acceleration
16:10-16:25 S9 Sunil Kumar
Low frequency vibrational modes in carbon nanotubes: terahertz
time domain spectroscopy
16:25-16:45 P1 Rema Krishnaswamy
Jamming and shear banding in two dimensional suspensions
16:45-17:00 S10 Surajit Saha
Phonon anomaly in pyrochlore spin-ice Dy2Ti2O7 and nonmagnetic
Lu2Ti2O7: A temperature dependent Raman and x-ray
study
17:00-17:15 S11 K Vijay Kumar
Brownian Inchworm Model of a Self-propelled particle
Day 2
(25/11/2008)
09:00-10:25 SESSION IV
Chair: V. Venkataraman

09:00-09:20 F7 Ramesh Chandra Mallik
Thermoelectric Properties of Co4Sb12 Skutterudite Materials with
In Addition
09:20-09:40 F8 Diptiman Sen
Scattering of electrons from an interacting region
09:40-09:55 S12 Prasad Perlekar
Statistically Steady Turbulence in Soap Films: Direct Numerical
Simulations with Ekman Friction
09:55-10:10 S13 Samriddhi Sankar Ray
Hyperviscosity, Bottlenecks and New Surprises in the Galerkintruncated
Burgers Equation
10:10-10:25 S14 Avatar Tulsi
General framework for quantum search algorithms
10:25-11:00 TEA
11:00-12:40 SESSION V
Chair: S. V. Bhat
11:00-11:20 F9 S. Ramakumar
Crystal Structures of native and substrate complex of an alkali
thermostable xylanase from an alkalophilic Bacillus sp. NG-27.
Structural insights into alkalophilicity.
11:20-11:40 F10 Arindam Ghosh
Intrinsic magnetism in high-mobility semiconductor – a bottom-up
route to spin-electronics?
11:40-11:55 S15 D. Samal
The incongruous observation of phase separation in La0.85
Sr0.15CoO3 spin –glass system
11:55-12:10 S16 Amrita Singh
New electrochemistry based route to Materials Engineering in
Nanoscale Systems
12:10-12:25 S17 M Suheshkumar Singh
Ultrasound-modulated Diffuse Optical Tomographic Imaging
System for Screening Breast Cancer
12:25-12:45 P2 Norio Kikuchi
A filament in an active medium: buckling, stiffening and negative
dissipation
VOTE OF THANKS BY CHAIRMAN

POSTERS
No
P1
P2
P3
P4
P5
P6
P7
P8
P9
P10
P11
P12
P13
P14
P15
P16
Name Title
Arjun Joshua and V. Venkataraman
Enhancement of sensitivity of detection of Kerr rotation by time averaging
Vikram Rathee, Sajal Kumar Ghosh, Rema Krishnaswamy, V. A. Raghunathan
and A. K. Sood
Reentrant phase behavior of a mixed surfactant system with strongly binding
counter-ions
Geetanjali, D. Banerjee and S V Bhat
Structural, magnetic and EMR studies of CaMnO3 nanoparticles
Sayak Ghoshal and P.S.Anil Kumar
Magnetic and Magnetotransport studies of ZnO films with and without intrinsic
magnetic moment
Sumilan Banerjee, Chandan Dasgupta, and T. V. Ramakrishnan
Ginzburg Landau Theory for Cuprate Superconductivity
Suropriya Saha and Sriram Ramaswamy
Non Equilibrium noise in electrophoresis: the micro-ion wind
Sakshath. S. and P. S. Anil Kumar
Magnetic Anisotropy in Epitaxial Fe/MgO films grown by Pulsed Laser
Deposition
Debangsu Roy, and P.S. Anil Kumar
Observation of the exchange spring behavior in hard-soft- ferrite nanocomposite
Biswanath Chakraborty, Anindya Das and A.K. Sood
Probing the local stress in Graphene by Raman Spectroscopy
Chinkhanlun Guite and V. Venkataraman
Electrical detection of spin polarized electrons in semiconductors using a radiofrequency
pick-up coil
Anupam Gupta, Prasad Perlekar, and Rahul Pandit
Polymer Addtives in Decaying Two-Dimensional Turbulence
Smarajit Karmakar, Chandan Dasgupta and Srikanth Sastry
Numerical study of a glass forming liquid in two dimensions to test the dimension
dependence of the Adam-Gibbs relation
Ramakanta Naik,R.Ganesan,K.S.Sangunni.
Compositional dependence of the optical changes in (As2S3)1-xSbx chalcogenide
film.
Nitin P. Lobo and K.V. Ramanathan
Measurement of Heteronuclear dipolar couplings- A systematic study of cross
polarization dynamics for Separated Local Field (SLF) experiments
S.M. Mohanasundaram and Arindam Ghosh
Detection of microcantilever deflection using electron transport measurements
Chandni U and Arindam Ghosh
A fluctuation-based probe to criticality in structural transitions

P17
P18
P19
P20
P21
P22
P23
P24
P25
P26
P27
P28
Jayakrishna Khatei and K.S.R. Koteswara Rao
Temperature dependent photoluminescence study in Hg1-xCdxTe (x~0.8) nano
and microcrystals
Alok Ranjan Nayak, T.K. Shajahan, and Rahul Pandit
The Dependance of Spiral-Wave Dynamics on Inhomogeneities in the TNNP
Model of Cardiac Tissue
Nitin Kumar, Sayantan Majumdar, Aditya Sood, Rama Govindarajan, Sriram
Ramaswamy and A.K. Sood
Motion of falling spheres and rising bubbles in a viscoelastic gel: spontaneous
oscillations and bursting
Sayantan Majumdar and A.K. Sood
Negative viscosity fluctuations and their universality in a driven repulsive
colloidal glass
Aditya A. Wagh, H.L.Bhat, P. S. Anil Kumar and Suja Elizabeth
MAGNETOTRANSPORT STUDIES OF FLOAT ZONE-GROWN Gd1-
xSrxMnO3 SINGLE CRYSTAL
Paramita Kar Choudhury, Debjani Bagchi, and Reghu Menon
Conformational modification by conjugation length and solvent in rigid-rod
organic semiconductor
K Jugeshwar Singh, G Clark, K P Ramesh and Reghu Menon
H-NMR and charge transport in metallic polypyrrole at ultra-low temperatures
and high magnetic fields
Atindra Nath Pal and Arindam Ghosh
Resistance noise in electrically biased bilayer graphene
Meghana Dharmik and Prabal Maiti
Structure and stability of carbon and boronnitride nanorings
R.Koushik and Arindam Ghosh
Conductivity noise in strongly correlated systems
Manas Khan and A. K. Sood
Out-of-Equilibrium Microrheology to Probe Directional Viscoelastic Properties
under Shear
Biswaroop Mukherjee, Prabal K. Maiti, Chandan Dasgupta and A. K. Sood
Jump reorientation of water molecules confined in narrow carbon nanotubes

TALK
ABSTRACTS

The surprisingly flattened dark matter halo of the Andromeda Galaxy
Chanda J. Jog
The rotation curve of a spiral galaxy is normally used to deduce its dark matter
halo content. Another complementary constraint is provided by the vertical scaleheights
of the interstellar gas, but this has not been exploited much in the literature.
We use both these for the nearby Andromeda galaxy to determine its halo density
distribution (Banerjee & Jog 2008, Astrophysical Journal, 685, 254). We
model the galaxy as a gravitationally coupled star-gas system responding to the
external force-field of the dark matter halo. We show that a highly flattened oblate
halo with an axis ratio of 0.4, and an isothermal density profile, provides the best
fit to the observed data. The flattened shape of the dark matter halo is a robust
result, and is strikingly different from the spherical shape generally assumed. This
has important implications for galaxy formation which will be discussed.
A similar approach has been applied to the low surface brightness galaxy UGC
7321 for which the scaleheight information is available. Here the best-fit result from
our model implies high gas dispersion, this could explain the low star formation seen
in this galaxy (Banerjee, Matthews & Jog 2008, Mon. Not. Roy. Astron.
Soc., submitted).
1

Novel Physics in Hetero-structures of Strongly Correlated
Materials
H. R. Krishnamurthy
Department of Physics, Indian Institute of Science
The study of hetero-structures constructed out of strongly correlated materials,
such as oxides, has been attracting a lot of attention recently. One of the reasons for
interest in these systems is that new physical phenomena emerge in these heterostructures
that are absent in the bulk materials they are composed from. I will review a
few recent examples, like the appearance of two-dimensional electron gases at the
interfaces between band and Mott insulators, and their low-temperature
superconductivity, and discuss the physics involved. I will end with a brief discussion of
our recent research [1], showing the possibility of another such striking, quantum
emergent phenomenon, namely that at sufficiently low temperatures, a finite width Mott
insulator sandwiched between two metallic leads could display perfect dc conductance.
[1] H. Zenia , J.K. Freericks, H. R. Krishnamurthy,Th. Pruschke : arXiv:0809.4993v1

Polymer nanocomposites near glass transition : Role of interface
S.Srivastava and J.K.Basu
Department of Physics
The unique optical, thermo mechanical, electronic properties of polymer nanocomposite
provide opportunities for better understanding of certain fundamental aspects of polymer
nanocomposite. Recent experiments show that such drastic change in properties results
due to possibility of the existence of a region with modified property at the nanoparticlepolymer
interface as well as due to confinement .Thermal property, importantly, Glass
transition is effected significantly which is an important property in determining the
suitability of a polymer nanocomposite for many application. Thus to understand the
dynamics of the polymer segments at interface needs to be probed with high resolution
technique to relate this to macroscopic properties like visco-elasticity, glass transition
(T g ), etc. To address this issue we have performed highly sensitive modulated differential
scanning calorimetry (MDSC) measurements of glass transition of
polymethylmethacrylate (PMMA) capped gold nanoparticles dispersed in same matrix.
Experiments have shown that T g decreases for non-interactive metal-polymer interface
and increases for the attractive interaction, however we have shown for the first time the
cross over in the sign of the shift of T g for a neutral polymer-metal interface[1]. The
dynamics of polymer segments at the metal - polymer interface can be controlled by the
variation of the interfacial width, σ, which is an important parameter to study
confinement effect on the polymer glass transition.. We have used a new parameter,
nanoparticle-polymer interfacial width, σ, in elucidating role of surface effects on glass
transition of polymers. Our results [2] show that interfacial width less than characteristic
length, ξ, results in reduction and more than it gives rise to enhancement in the glass
transition temperature of the polymer.
To study the effect of interface on the dynamics of such systems we have performed X-
ray photon correlation spectroscopy measurements . Measurements performed at various
temperatures around the glass transition temperature of the polymer nanocomposite
powders revealed intriguing differences in the respective wave vector dependent
intermediate scattering function elucidating the role of interface morphology [3] in
determining the relaxation dynamics, especially a gel - to –attractive glass transition,
References:
1). S.Srivastava and J.K. Basu, J. Nanoscience and Nano Technology 7, 2101, 2007.
2). S.Srivastava and J.K. Basu, Physical Review Letter 98, 165701, 2007.
3). S. Srivastava , A. K. Kandar, and J. K. Basu, M.K. Mukhopadhyay, and S. Narayanan
(Manuscript under review).

Observation of low temperature Persistent Photoconductivity in flower
shaped dendritic PbS structures
Naresh Babu Pendya, K.S.R.K.Rao
Semiconductor Lab, Department of Physics, I.I.Sc. Bangalore-560012
Abstract
Persistent Photoconductivity (PPC) has been observed in flower shaped PbS dendrite
structures upto 220 o K for first time. Potential variation due to the presence of various
sized particles might be the cause for the PPC. PPC relaxation behavior can be well
β
described by a stretched-exponential function I ( t) = I (0)exp[ −( t τ) ]( β ≺ 1) where
τ is the relaxation time constant and β the decay exponent. The photocurrent build-up
curves can be described by an equivalent stretched-exponential function
I ( t) = I [1 −exp( − ( αt) β ] . Along with the PPC, we also observed Negative Persistent
ppc
max
Photoconductivity (NPPC) below 40 o K, and above which it is Positive Persistent
Photoconductivity (PPPC). A metastable state at 40 K might be the reason for the above
observations. The exact nature of the metastable state is not known at present. These
primary results certainly encourage us to do more measurements on this system as well
on other dendrite structures.
ppc
ppc

Fabrication and Electrical Characterization of Charge Transfer Molecular Wires
T.Phanindra Sai *, 1 and A.K.Raychaudhuri 1, 2
1 Department of Physics, Indian Institute of Science, Bangalore-560012
2 Unit for Nanoscience, S.N.Bose National Center for Basic Sciences,
Salt Lake Kolkata-700 098
----------------------------------------------------------------------------------------------------
The aim of the present work was to grow isolated molecular wires of charge transfer complex and
study their electrical and transport properties. The molecular wires were grown using thermal coevaporation
technique, where the donor and acceptor charge transfer molecules are simultaneously
evaporated form two different crucibles in a vacuum chamber on to a lithographically patterned
substrates. An electric field is also applied between anode and cathode to enhance the growth of the
molecular wires. The donor materials used were TMTTF and TTF and the acceptor was TCNQ. The
substrate is also maintained at a constant temperature during evaporation. SEM images of the molecular
wires grown across wider and larger electrode gaps showed that each molecular wire consists of bunches
of smaller wires of diameter 200 nm in the case of TMTTF-TCNQ samples and even 50 nm in the case
of TTF-TCNQ wires. We are interested in studying the properties of the single molecular wire of these
charge transfer molecules of different widths ranging from 500 nm down to 50 nm. To fabricate single
molecular wires e beam lithography was used to write contact pads with reduced electrode gaps and
electrode widths onto silicon oxide substrates. A resistance vs temperature measurement of the grown
molecular wires shows a semiconductor like behavior whereas previous studies on single crystals of
TTF-TCNQ molecules have shown metallic behavior. This happens because the wires grown by thermal
evaporation does not have the 1:1 stiochiometry due to different vapor pressures of TTF and TCNQ
molecules.
* Tetrathiafulvalene (TTF), Tetracayanoquinodimethane (TCNQ), Trimethyltetrathiafulvalene (TMTTF).

Growing length and time scales in glass forming liquids
Smarajit Karmakar 1 , Chandan Dasgupta 1,2 , Srikanth Sastry 2
1 CCMT, Department of Physics, Indian Institute of Science, Bangalore
2 Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore
Explaining the enormous increase in the viscosity and relaxation time of a liquid
upon supercooling is essential for an understanding of the structural glass transition.
Although the notion of a growing length scale of “cooperatively rearranging regions”
is often invoked to explain dynamical slow down, the role of length scales relevant
to glassy dynamics is not well established. Recent studies of spatial heterogeneity
in the local dynamics provide fresh impetus in this direction. Using finite-size
scaling for the first time for a realistic glass former, we establish that the growth
of dynamical heterogeneity with decreasing temperature is governed by a growing
dynamical length scale. However, the dependence of the simultaneously growing
relaxation time on system size does not exhibit the same scaling behaviour as the
dynamical heterogeneity. We show that the relaxation time is instead determined,
for all studied system sizes and temperatures, by the configurational entropy, in
accordance with the Adam-Gibbs relation, but in disagreement with the prevailing
belief that the configurational entropy is not relevant above the critical temperature
of mode coupling theory. These results provide new insights into the dynamics of
glass-forming liquids and pose serious challenges to existing theoretical descriptions.

Nanophotonics with Quantum Dot Arrays and Optical Near Fields.
Haridas M and Jaydeep Basu
Nanophotonics, which involves local electromagnetic interactions between nanometerscale
materials and an optical near field (ONF), promises to open the doors towards next
generation technology for quantum information processing using light and quantum
devices. ONF's are characterised by the presence of optical fields with high lateral spatial
frequencies able to excite surface states not accessible by means of conventional far-field
optical excitations including possibilities of exciting dipole-forbidden states. Scanning
Near field Optical Microscopy (SNOM) is recently developed experimental technique
used to produce such ONF and combines the advantages of the relatively new scanning
probe based microscopy, with the rich and well developed field optical spectroscopy.
SNOM has been widely used to study single and coupled quantum dots as well as
metallic nanostructures. Most of the experimental and theoretical studies limited to
studying very small number of ideal quantum dots which are homogeneous and are
arranged an in an ordered manner without disorder. However, for any potential device
applications, the real system would involve a large array of QDs in which both
inhomogenity and disorder would be present. Studying the coupling of ONF with such a
QD array would lead to a understanding of not only the differences with the far- field
spectra but also the role of disorder and inhomogenity in the near field spectra of large
scale QD arrays.
Here we will discuss the use of SNOM to study coupling between ONF and excitons in
large scale arrays of CdSe QD. The PL spectra collected in SNOM mode and in confocal
mode (far field) from the CdSe based QD arrays shows striking differences. We also
compare the spatially resolved PL spectra collected in SNOM mode from different region
of the QD array and find coupling fine structure in such spectra. We discus the possible
sources of such fine structures and point to the need for a unified theory to treat the ONF
and excitons in QD arrays as a single coupled quantum system.
Reference:
1. Haridas M and J. K. Basu (submitted)
2. Haridas M and J. K. Basu (manuscript in preparation)
3. Haridas M and J. K. Basu (manuscript in preparation)

Diffuse optical tomographic non-invasive breast and brain imager using a single laser
light source
S. K. Biswas 1 , K. Rajan 1 , and R. M. Vasu 2
Department of Physics 1
Department of Instrumentation 2
Indian Institute of Science, Bangalore, 560012 India.
Near-Infrared (NIR) diffuse optical tomography technique has the capability of providing good
quantitative reconstruction of distribution of tissue absorption and scattering parameters with additional
inputs such as input and output modulation depth and photon leakage correction through
the measurement process. The light transport through a tissue is diffusive in nature and can be
modeled using diffusion equation (DE). The optical parameters of the inhomogeneity can be recovered
if they are close to the optical properties of the background. Diffusion equation for photon
transport is solved using Finite Element Method (FEM) and Jacobian is modeled for reconstructing
the optical parameters of the object. We study the development and performance of DOT system
using 100MHz modulated single laser source and multiple detectors. The theory has been evolving
continuously over the past 15 years but very few has come forward to implement and handover a
product to human society. Diffuse Optical Tomography (DOT) is a promising tool for non-invasive
imaging of deep tissue. To reduce the gap between the theory and the experiment we have calculated
the 2-D input modulation depth from 3-D diffusion to model the 2-D diffusion of photons. The
photon leakage when light traverses from fiber tip to the phantom is estimated using a solid angle
model. We study the development and performance of DOT system using 100MHz modulated single
laser source and multiple detectors. The experiment is carried out with 5mm, 6mm 8mm (diameter)
inhomogeneities with absorption coefficient almost three times as that of the background. The
experimental result shows that our single source system with additional inputs such as separated
2-D input/output modulation depth from 3-D diffusion and weighted air fiber interface correction is
capable of detecting 5mm 6mm and 8mm separately and can identify the size difference of multiple
inhomogeneities with zero localization error.
FIG. 1: Reconstructed results from Experimental data for single as well as multiple inhomogeneities with different sizes. The
size of inhomogeneities are 5mm shown in Fig.1:a and 6mm , 8mm shown in Fig.1b . The reconstructed image shows the exact
positions of inhomogeneities as it were in the phantoms that we used in our experiment.

High pulsed field magnetotransport and hole mobility in HgCdTe
Murthy O.V.S.N., V. Venkataraman, R.K. Sharma
Mercury Cadmium Telluride, despite competition, is still a material of choice for
manufacturers of infrared detectors especially in the 10 μm region due to its high
efficiency. Being a narrow gap semiconductor, its physics is much different from the
Si/GaAs genus. A study on magnetotransport in bulk as well as epilayers of HgCdTe at
both low and high temperatures is presented.
We have designed, constructed and calibrated high performance pulsed magnets
operating upto 17T from 77K-300K and 12T down to 4K for magnetotransport
measurements [1]. Data is obtained using a fast A/D card and analyzed using digital lockin
method.
The composition of the samples under study is determined using optical absorption
measurements. High magnetic fields are required to probe low mobility holes owing to
the electronic domination of conductivity at low B even in p-type samples. Multicarrier
analysis is used to extract mobilities and densities from the measured mixed conductivity
tensor upto 15T. Hole mobility at higher temperatures from 200K-300K in magnetic
fields is investigated using a hybrid method by various scattering mechanisms. We have
solved Boltzmann transport equation numerically without relaxation time approximation
[2] to include polar optical phonon scattering. Other scattering mechanisms taken into
account with or without using relaxation time approximation [3] are: ionized impurity,
nonpolar optical, acoustic, dislocation, alloy disorder and piezoelectric. Results are
presented comparing our data with the calculated mobility.
[1] Murthy O.V.S.N., Venkataraman V., Rev. Sci. Instrum. 78, 113905 (2007)
[2] Rode, D.L., Phys. Rev. B 2, 1012 (1970)
[3] Yadava, R.D.S. et al, J. Electron Mater. 23, 1359 (1994)

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Force Induced DNA Melting
Mogurampelly Santosh † and Prabal K Maiti *
Center for Condensed Matter Theory, Department of Physics,
Indian Institute of Science, Bangalore­12
Abstract
When pulled along the axis, double­strand DNA undergoes a large conformational
change and elongates roughly twice its initial contour length at a pulling force about
70 pN. The transition to this highly overstretched form of DNA is very cooperative.
Applying force perpendicular to the DNA axis (unzipping), double­strand DNA can
also be separated into two single­stranded DNA which is a fundamental process in
DNA replication. We study the DNA overstretching and unzipping transition using
fully atomistic molecular dynamics (MD) simulations and argue that the
conformational changes of double strand DNA associated with either of the above
mentioned processes can be viewed as force induced DNA melting. As the force at
one end of the DNA is increased the DNA start melting abruptly/smoothly after a
critical force depending on the pulling direction. The critical force f m , at which DNA
melts completely decreases as the temperature of the system is increased. The melting
force in case of unzipping is smaller compared to the melting force when the DNA is
pulled along the helical axis. In the cases of melting through unzipping, the doublestrand
separation has jumps which correspond to the different energy minima arising
due to different base pair sequence. The fraction of Watson­Crick base pair hydrogen
bond breaking as a function of force does not show smooth and continuous behavior
and consists of plateaus followed by sharp jumps.
†
santosh@physics.iisc.ernet.in
*
maiti@physics.iisc.ernet.in

Ultrafast electron dynamics and cubic optical nonlinearity of single
and double walled carbon nanotubes.
N. Kamaraju, Sunil Kumar, B. Karthikeyan and A. K. Sood
Department of Physics, Centre for Ultrafast Laser Applications, Indian Institute of
Science, Bangalore-560012.
We have studied cubic optical nonlinearities of single walled carbon nanotube (SWNT)
suspensions and a free standing thin film of double walled carbon nanotubes (DWNT) using 790
nm, 80 femtosecond light pulses in open and closed aperture z-scan experiments. The nanotube
suspensions were prepared in water using sodium dodecyl sulphate [1] and by microwave
treatment with amide functionalization [2]. We have developed a modified theoretical expression
to analyze the z-dependent transmission (both open and closed aperture) in the saturable limit.
This gives a value of Im (χ (3) ) ~ 4.9 x 10 -10 (0.45 x10 -10 ) esu and Re (χ (3) ) ~ 5.4 x 10 -10 (2.2 x10 -9 )
esu for SWNT (DWNT). Degenerate femtosecond pump-probe experiments (790nm, 80 fs) to
investigate [3] the optical switching time and the underlying ultrafast electron dynamics in
DWNT show ultrafast (97 fs) photo bleaching followed by a photo-induced absorption with a
slow relaxation of 1.8 ps, whereas microwave treated SWNT suspension shows a bi-exponential
ultrafast photo-bleaching with time constants of 160 fs (130 fs) and 920 fs (300 fs) for water
soluble (amide functionalized) nanotubes.
We thank Department of Science and Technology for financial support. This work was
done in collaboration with Bhalchandra Kakade, Vijayamohanan K. Pillai, Alexander Moravsky,
R. O. Loutfy, Srini Krishnamoorthy, Shekhar Guha and C. N. R. Rao.
Reference:
1. “Large nonlinear absorption and refraction coefficients of carbon nanotubes estimated
from femtosecond z-scan measurements”, N. Kamaraju, Sunil Kumar, Srinivasan
Krishnamurthy, Shekhar Guha, A. K. Sood, C. N. R. Rao. Appl. Phys. Lett. 91, 251103
(2007).
2. “Ultrafast electron dynamics and cubic optical nonlinearity of free standing thin film of
double walled carbon nanotubes”, N. Kamaraju, Sunil Kumar, B. Karthikeyan,
Alexander Moravsky, R. O. Loutfy and A. K. Sood. Appl. Phys. Lett. 93, 091903 (2008).
3. “Ultrafast switching time and third order nonlinear coefficients of microwave treated
single walled carbon nanotube suspensions”, N Kamaraju, Sunil Kumar, B. Karthikeyan,
Bhalchandra Kakade, Vijayamohanan K. Pillai and A. K. Sood, J. Nanoscience and
Nanotech. (2008).

Nonequilibrium Fluctuations in Sheared
Jammed States
A.K. Sood
Department of Physics, Indian Institute of Science
Bangalore 560 012, India.
Recently we have shown that the shear rate at a fixed shear stress in a
micellar hexagonal phase exhibits large fluctuations, including several negative
values [1]. The probability distribution functions (PDF’s) of the global power
flux to the system derived from the shear rate fluctuations are Gaussian or non-
Gaussian, depending on the external drive (applied stress) on the system. In
both cases, the PDF is consistent with the Gallavotti-Cohen steady state
fluctuation theorem. We show that an effective temperature of the jammed state
can be measured using fluctuation theorem. Interestingly, the non-Gaussian PDF
of the global power flux to the system matches exactly with one of the universal
extreme value distribution.
1. S. Mazumdar and A.K. Sood, Phys. Rev. Lett. 101, 78301 (2008).

Extended Einstein-Hilbert (E-H) action and the emergence of Riccions as
cosmic dark matter and consequent cosmic acceleration
K.P.Sinha
INSA Honorary Scientist
Department of Physics
Indian Institute of Science
Bangalore 560 012.
Abstract:
When higher-order curvature terms are added to E-H action Ricci
scalars behave as a massive physical field and obey Klein-Gordon type
equation. These particles are called Riccions. The role of riccions
as cosmic dark matter is explored. It is found that the universe will
accelerate when appropriate conditions are satisfied particularly in
the later period of the evolution of the universe.
The dual nature of the Ricci scalar in the present model solve
many problems such as the removal of the gravitation singularity1,
creation of spinless particles2 , the creation of spin particles and
antiparticles3 and the dominance of baryonic matter besides being the
source of dark matter4
References:
1. S.K.Srivastava and K.P.Sinha, Phys. Lett. B 307, 40 (1993)
2. K.P.Sinha and S.K.Srivastava, Pramana 44, 333 (1995)
3. S.K.Srivastava and K.P.Sinha, Mod. Phys. Lett A 12, 2933 (1997)
4. S.K.Srivastava and K.P.Sinha, Mod. Phys. Lett A. (in press)

Low frequency vibrational modes in carbon nanotubes:
terahertz time domain spectroscopy
Sunil Kumar 1 , N. Kamaraju 1 , Marc Tondusson 2 , E. Freysz 2 and A. K. Sood 1,*
1 Department of Physics and Center for Ultrafast Laser Applications,
Indian Institute of Science, Bangalore 560 012, India
2 CPMOH, Universite de Bordeaux I, 351, Cours de la liberation, 33405 Talence cedex, Fance
* Electronic address: asood@physics.iisc.ernet.in
Ultrafast terahertz time domain spectroscopy (THz-TDS) has been used to study the far
infrared (FIR) optical properties of double walled carbon nanotubes (DWNTs) in the 0.1-
3.0 THz frequency range. The 200 nm freely standing DWNT film, used in our
experiments works as a THz filter in the time domain as the input THz power is cut by
almost half while the spectral transmission remains almost constant in the 0.1-2.0 THz
range. This feature, usually expected for metallic substrates with patterned whole arrays
[1] or metamaterials with artificial structures [2], suggests a possible application of such
films of carbon nanotubes (CNTs) for real time control and modulation of THz radiation.
The spectral dielectric response of the film shows small but distinct resonant dispersive
features at frequencies, 0.46 and 0.76 THz related to the very low frequency flexural
modes of vibration around the tube axis. Such low frequency phonon modes in CNTs had
been predicted theoretically [3, 4] but so far could not be detected experimentally. In
addition we have observed a broad absorption band at around 1.45 THz similar to that
seen in single walled CNTs (SWNTs) attributed to the electronic excitation across the
FIR band gap induced by intertube coupling and curvature in bundles of metallic
nanotubes [5]. The optical conductivity was measured to be very high, of the order of
2x10 14 sec -1 which confirms the metallic nature of the film (optical conductivity of metals
~ 10 16 sec -1 ).
References
1. C. L. Pan, C. F. Hsieh, R. P. Pan, M. Tanaka, F. Miyamaru, M. Tani, M. Hangyo, Opt.
Exp. 13, 3921 (2005).
2. H. T. Chen, W. J. Padilla, J. M. O. Zide, A. C. Gossard, A. J. Taylor, Nature 444, 597
(2006).
3. H. Suzuura, T. Ando, Phys. Rev. B 65, 235412 (2002).
4. G. D. Mahan and Gun Sang Jeon, Phys. Rev. B 70, 075405 (2004).
5. M. Ouyang, J. L. Huang, C. L. Cheung, C. M. Lieber, Science 292, 702 (2001).

Jamming and shear banding in two dimensional suspensions
Sayantan Majumdar, Rema Krishnaswamy and A. K. Sood
The flow behaviour of jammed systems which exhibit a solid-like elastic behaviour at
low shear stress and flow above a critical yield stress is often described by
phenomenological models, where a homogenous flow is predicted at a fixed shear
stress. Recent studies however, indicate that most jammed systems unjam through the
formation of shear bands where only part of the system flows. Two dimensional (2D)
colloidal suspensions where the flow behaviour can be visualized relatively easily are
eminently suited for understanding the role of the microstructure in determining the
jamming or yielding behaviour. I will discuss some of our recent studies where we
investigate the viscoelastic and flow behaviour of dense monodisperse and bidisperse
2D colloidal suspensions formed at fluid interfaces by combining surface rheology
with optical microscopy.
In densely packed colloidal monolayers at packing fractions > 0.8, the shear rate at a
fixed shear stress exhibits large fluctuations with positive and negative values. The
validity of Steady State Fluctuation Relation in these sheared two dimensional
suspensions will also be examined.

Phonon anomaly in pyrochlore spin-ice Dy 2 Ti 2 O 7 and non-magnetic Lu 2 Ti 2 O 7 :
A temperature dependent Raman and x-ray study
Surajit Saha, 1 Surjeet Singh, 2 B. Dkhil, 3 S. Dhar, 4 R. Suryanarayanan, 2 G. Dhalenne, 2
A. Revcolevschi, 2 and A. K. Sood 1
1 Department of Physics, Indian Institute of Science, Bangalore, India.
2 Laboratoire de Physico-Chimie de l’Etat Solide,Universite Paris-Sud, Orsay, France.
3 Laboratoire Structures, Ecole Centrale Paris, Chatenay-Malabry Cedex, France and
4 Tata Institute of Fundamental Research, Mumbai, India
Abstract
We present here temperature-dependent Raman, x-ray diffraction and specific heat
studies between room temperature and 12 K on single crystals of spin-ice pyrochlore
compound Dy 2 Ti 2 O 7 and its non-magnetic analogue Lu 2 Ti 2 O 7 . Raman data show a “new”
band not predicted by factor group analysis of Raman-active modes for the pyrochlore
structure in Dy 2 Ti 2 O 7 , appearing below a temperature of T c =110 K with a concomitant
contraction of the cubic unit cell volume as determined from the powder x-ray diffraction
analysis. Low temperature Raman experiments on O 18 -isotope substituted Dy 2 Ti 2 O 7
confirm the phonon origin of the “new” mode. These findings, absent in Lu 2 Ti 2 O 7 ,
suggest that the room temperature cubic lattice of the pyrochlore Dy 2 Ti 2 O 7 undergoes a
“subtle” structural transformation near T c . We find anomalous red-shift of some of the
phonon modes in both the Dy 2 Ti 2 O 7 and the Lu 2 Ti 2 O 7 as the temperature decreases, which
is attributed to strong phonon-phonon anharmonic interactions.

Brownian Inchworm Model of a Self-propelled particle
K Vijay Kumar, 1, ∗ Adrian Baule, 2, † Sriram Ramaswamy, 1, ‡ and Madan Rao 3, §
1 CCMT, Department of Physics, Indian Institute of Science, Bangalore 560012, India.
2 The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
3 Raman Research Institute, Bangalore 560080, India.
Directed motion without an imposed external gradient is seen not only in living systems but
also in agitated granular matter. The essential ingredients are an external energy input and
an inherent asymmetry. Unlike traditional “Brownian ratchet models”of directed motion,
the asymmetry of interest in the above systems is internal to the motile objects, and does
not lie in an external periodic potential.
In this work, we present a Brownian inchworm model of a self-propelled elastic dimer
in the absence of an external potential. Nonequilibrium noise together with a stretchdependent
damping form the propulsion mechanism. The crucial asymmetry is in the
stretch-dependence of the damping coefficients. Our model connects three key nonequilibrium
features – position-velocity correlations, a nonzero mean internal force, and a drift
velocity. Our analytical results, both perturbative calculations and an exact solution, display
striking current reversals and compare very well with numerical simulations [1, 2]. The
model unifies the propulsion mechanisms of DNA helicases, polar rods on a vibrated surface,
crawling keratocytes and Myosin VI.
∗
Electronic address: vijayk@physics.iisc.ernet.in
† Electronic address: abaule@rockefeller.edu
‡ Electronic address: sriram@physics.iisc.ernet.in;
Also at CMTU, JNCASR, Bangalore 560064, India.
§ Electronic address: madan@rri.res.in; Also at NCBS (TIFR), Bangalore 560065, India.
[1] K Vijay Kumar, S. Ramaswamy and M. Rao, Phys. Rev. E, 77, 020102(R), (2008).
[2] Adrian Baule, K Vijay Kumar and Sriram Ramaswamy, J. Stat. Mech., P11008 (2008).

Thermoelectric Properties of Co 4 Sb 12 Skutterudite Materials with In Addition
Ramesh Chandra Mallik * , Christian Stiewe, Gabriele Karpinski, Ralf Hassdorf, Eckhard Müller
German Aerospace Center (DLR), Institute of Materials Research,
D-51170 Cologne, Germany
* Department of Physics, Indian Institute of Science, Bangalore, 560 012, India
Abstract
The properties of Co 4 Sb 12 with various In additions were studied. X-ray diffraction
technique used for structural and phase analysis. The homogeneity and morphology of
the samples were observed by the Seebeck microprobe and scanning electron
microscopy, respectively. The temperature dependence of the Seebeck coefficient,
electrical and thermal conductivity was measured from room temperature up to 673 K.
The Seebeck coefficient of all In-added Co 4 Sb 12 materials was negative. When the In
concentration increases, then the Seebeck coefficient decreases. The samples with In
additions above the limit (x= 0.22) show an even lower Seebeck coefficient due to the
formation of secondary phases: InSb and CoSb 2 . The temperature variation of the
electrical conductivity is semiconductor-like. The thermal conductivity of all the samples
decreases with temperature. The central region of the In 0.4 Co 4 Sb 12 ingot shows the lowest
thermal conductivity probably due to the combined effect of (a) rattling due to maximum
filling and (b) the presence of a small amount of fine -dispersed secondary phases at the
grain boundaries. Thus, regardless of the non-single-phase morphology, a promising ZT
value of 0.96 at 673 K has been obtained with an In addition above the filling limit.
Email: rcmallik@physics.iisc.ernet.in

Scattering of electrons from an interacting region
Diptiman Sen (CHEP)
We study the problem of transmission of electrons through a region where they
interact with each other. The two-particle problem turns out to completely solvable. We
show that if there is no other source of scattering, the interactions always reduce the
conductance from the value of 2e^2/h. But if the region itself causes scattering,
interactions can either increase or decrease the conductance. We discuss the possibility of
two-particle resonance, in which two particles with a particular value of the total energy
can transmit through the region even though they cannot individually do so.
Collaborators:
Abhishek Dhar and Dibyendu Roy (RRI) and Abhiram Soori

Statistically Steady Turbulence in Soap Films: Direct Numerical Simulations with
Ekman Friction
Prasad Perlekar 1, ∗ and Rahul Pandit 1, †
1 Centre for Condensed Matter Theory, Department of Physics,
Indian Institute of Science, Bangalore 560012, India.
We present a detailed direct numerical simulation (DNS) designed to investigate the combined
effects of walls and Ekman friction on turbulence in forced soap films. We concentrate on the
forward-cascade regime and show how to extract the isotropic parts of velocity and vorticity structure
functions and thence the ratios of multiscaling exponents. We find that velocity structure functions
display simple scaling whereas their vorticity counterparts show multiscaling; and the probability
distribution function of the Weiss parameter Λ, which distinguishes between regions with centers
and saddles, is in quantitative agreement with experiments.
∗ Electronic address: perlekar@physics.iisc.ernet.in
† Electronic address: rahul@physics.iisc.ernet.in;
also at Jawaharlal Nehru Centre For Advanced Scientific Research, Jakkur, Bangalore, India

Hyperviscosity, Bottlenecks and New Surprises in the Galerkin-truncated Burgers
Equation 1
Samriddhi Sankar Ray
It is shown that the replacement in hydrodynamical equations of the usual dissipation by a high
power α of the Laplacian leads asymptotically to truncating the dynamics to a a finite number
of Fourier modes. When this number is large, a range of thermalized modes appear through the
mechanism discovered by Cichowlas et al. The dynamics at small and intermediate wavenumbers
is governed by the ordinary Navier–Stokes equations but a huge bottleneck in thermal equilibrium
with Gaussian statistics is present at large wavenumbers. The usual (α = 1) bottleneck can be
viewed as an aborted thermalization. Practical implications for turbulence modelling are discussed.
We then discuss surprises in the Galerkin-truncated Burgers Equation.
1. Hyperviscosity, Galerkin truncation and bottlenecks in turbulence,
U. Frisch, S. Kurien, R. Pandit, W. Pauls, Samriddhi Sankar Ray, A. Wirth, and J-Z Zhu.
Phys. Rev. Lett. 101, 144501.

General framework for quantum search algorithms
Avatar Tulsi
Department of Physics, Indian Institute of Science, Bangalore-560012, India.
Grover’s quantum search algorithm drives a quantum computer from a
prepared initial state to a desired final state by using selective transformations
of these states. We present a framework when one of the selective
transformations is replaced by a more general unitary transformation. Our
framework encapsulates several previous generalizations of Grover’s algorithm
like Kato’s algorithm, Ambainis’ algorithm for element distinctness
problem, spatial search algorithms, and quantum random walk search algorithms.
Our framework also explains the phase-matching condition.
We discuss two applications of our framework. The first one is related
to the problem of two-dimensional spatial search. The previous algorithms
take √ N ln N steps to solve this problem, and it was an open question
whether the performance can be improved. Our framework allows us to
design a faster algorithm that solves the problem in √ N ln N steps. The
second application is a better quantitative understanding of adiabatic search
algorithms.
References
[1] General framework for quantum search algortihms
Avatar Tulsi, quant-ph/0806.1257, Accepted for publication in Phys. Rev. A.
[2] Faster quantum walk algorithm for the two-dimensional spatial search
Avatar Tulsi, Phys. Rev. A 78, 012310 (2008).
[3] Adiabatic quantum computation with a one-dimensional projector Hamiltonian.
Avatar Tulsi, quant-ph/0806.0385, Accepted for publication in Phys. Rev. A.
1

Crystal Structures of native and substrate complex of an
alkali thermostable xylanase from an alkalophilic Bacillus
sp. NG-27. Structural insights into alkalophilicity.
Ramakumar, S.
Department of Physics
Indian Institute of Science, Bangalore – 560012, INDIA
Crystal structures are known for several glycosyl hydrolase family 10 (GH10) xylanases.
However, none of them is from an alkalophilic organism that can grow in alkaline conditions.
We have determined the crystal structures at 2.2 Å of a GH10 extracellular endoxylanase
(BSX) from an alkalophilic Bacillus sp. NG-27, for the native and the complex enzyme with
xylosaccharides. The industrially important enzyme is optimally active and stable at 343 K
and at a pH of 8.4. Comparison of the structure of BSX with those of other thermostable
GH10 xylanases optimally active at acidic or close to neutral pH showed that the solvent
exposed acidic amino acids. Asp and Glu, are markedly enhanced in BSX, while solventexposed
Asn was noticeably depleted. The BSX crystal structure when compared with
putative three-dimensional homology models of other extracellular alkalophilic GH10
xylanases from alkalophilic organisms suggests that a protein surface rich in acidic residues
may be an important feature common to these alkali thermostable enzymes. A comparison of
the surface features of BSX and of halophilic proteins allowed us to predict the activity of
BSX at high salt concentrations, which we verified through experiments. This offered us
important lessons in the polyextremophilicity of proteins, where understanding the structural
features of a protein stable in one set of extreme conditions provided clues about the activity
of the protein in other extreme conditions. The work brings to the fore the role of the nature
and composition of solvent-exposed residues in the adaptation of enzymes to polyextreme
conditions, as in BSX.

Intrinsic magnetism in high-mobility semiconductor – a bottom-up route to spinelectronics?
Arindam Ghosh
Ultra high-mobility GaAs/AlGaAs heterostructures are excellent systems for simulating
elementary magnetic interactions with great control. The usual methods of generating magnetism in these
semiconducting systems are two-fold: (1) defining quantum dot assemblies where each dot contains an odd
number of electrons so that they play the role of d-electrons embedded in a metallic matrix, or (2) doping
GaAs with magnetic atoms such as Mn. Here we propose a new route towards achieving a long-range
magnetism in GaAs/AlGaAs heterostructures that does not require either formation of quantum dots or
external doping of magnetic atoms. The idea is based on a two-component nature of background potential
fluctuations in modulation-doped GaAs/AlGaAs systems which naturally trap localized spins at specific
values of conduction electron density. A surface gate can modulate the mutual interaction between the
spins, making the magnetic state tunable electrically. Although the present devices required the
experiments to be carried out at sub-Kelvin temperature range, our experiments suggest that such a model
can be utilized in realizing spin field-effect transistors in low-dimensional semiconductors over a wide
parameter range.
Ref:
[1] A. Ghosh et al., Phys. Rev. Lett. 92, 116601 (2004);
[2] A. Ghosh et al., Phys. Rev. Lett. 95, 066603 (2005).
[3] C. Siegert, A. Ghosh, M. Pepper, I. Farrer and D. A. Ritchie, Nature Physics 3, 315 (2007).
[4] C. Siegert, A. Ghosh, M. Pepper, I. Farrer, D. A. Ritchie, D. Anderson and G. A. C. Jones, Phys. Rev. B
(2008).

The incongruous observation of phase separation in La 0.85 Sr 0.15 CoO 3
spin –glass system
D. Samal a , C. Shivakumara b and P.S. Anil Kumar a
a Department of Physics, Indian Institute of Science, Bangalore, 560012, India
b Solid State and Structural Chemistry Unit, Indian Institute of Science
Phase separation in hole-doped Cobaltites (La 1-x Sr x Co x O 3 ) is drawing renewed interest recently.
In particular, the magnetic behavior of La 0.85 Sr 0.15 CoO 3 has been subjected to a controversial
debate for the last several years; while some groups show evidence for phase separation, others
show spin glass behavior. An attempt is made to resolve the controversy related to “phase
separation versus spin glass” behavior in this compound. Here, we present the results of
comprehensive investigation of dc magnetization, ac susceptibility, and magnetotransport
properties of La 0.85 Sr 0.15 CoO 3 samples. We contemplate that the phase separation in
La 0.85 Sr 0.15 CoO 3 is neither intrinsic nor inherent but it is a consequence of the preparation
conditions. It is realized that low temperature annealed sample (LTA) shows phase separation
where as the high temperature annealed (HTA) sample shows pure spin glass behavior. The
Brillouin like behavior of field cooled dc magnetization with temperature and apparently no
frequency dependent peak shift in ac susceptibility for LTA sample characterizes it to be of
ferromagnetic like where as a kink in field cooled dc magnetization and considerable amount
(~3K) of frequency dependent peak shift in ac susceptibility for HTA sample characterizes it to
be a pure spin glass state. The magneto transport properties show that the HTA sample is more
semiconducting as compared to LTA sample. This is interpreted in terms of presence of isolated
as well as coalescing metallic ferromagnetic clusters in case of LTA sample. Both LTA as well as
HTA samples exhibit glassy transport phenomena i.e. glassy response to application or removal
of application of magnetic field with respect to time. The magnetoresistance at 10K for HTA
sample exhibits a huge value (~65%) as compared to the LTA sample and it monotonically
decreases with rise in temperature. Such a high value of MR in case of HTA sample is strongly
believed due to spin dependent part of random potential distribution. Further, the slow decay of
remnant magnetization with progress of time and existence of hysteresis at higher temperatures
(up to 200K) in case of LTA sample as compared to HTA sample clearly unveils different
magnetic states associated with them.
e-mail: debphy@physics.iisc.ernet.in

New electrochemistry based route to Materials Engineering in Nanoscale Systems.
Amrita Singh and Arindam Ghosh
Department of Physics, Indian Institute of Science, Bangalore, 560012
By appropriate engineering of electro-deposition technique, we have realized silver nanowires (AgNWs) in both hcp
and fcc phase at room temperature. The nanowires stabilized in high energy 4H phase [1], exhibit some exotic
properties. The measured noise level is heavily suppressed in 4H AgNWs as compared to fcc silver nanowires which
is attributed to restricted dislocation dynamics in hexagonal crystal structure [2]. The time resolved transmission
electron microscopy (TEM) shows a kinemetically new growth mechanism during electro-deposition. We observe a
temperature independent noise behavior in hcp AgNWs, which is uncommon for metals. Moreover, these nanowires
also exhibit a temperature induced phase transformation and acquire an unconventional fcc phase at low
temperatures, which is supported by temperature dependent TEM measurement, higher order resistance fluctuation
spectroscopy and Differential Scanning Calorimetry. Thus, the electron transport results pave a new understanding
of the crystal structure dependent microscopic origin of noise in single crystal nanowires and our growth
technique promises to produce high quality nano-materials with unprecedented control on its electrical and structural
properties.
[1] Amrita Singh and Arindam Ghosh, J. Phys. Chem. C, 112, 3460-3463, 2008.
[2]Amrita Singh, T. Phanindra Sai and Arindam Ghosh, Applied Physics Letters 93, 102107 (2008).

Ultrasound-modulated Diffuse Optical Tomographic Imaging System for Screening
Breast Cancer
M Suheshkumar Singh and K Rajan
Department of Physics, Indian Institute of Science
Bangalore-560012, India.
R M Vasu
Department of Instrumentation, Indian Institute of Science
Bangalore-560012, India.
Near-Infrared (NIR) diffuse optical tomography (DOT) has been a promising tool for non-invasive
imaging of optical parameters of tissues inside body over the past 15 years. Unfortunately, due
to diffusive nature of light, sophisticated reconstruction algorithms are required to achieve good
imaging depth and a reasonable resolution. Ultrasound (US), on the otherhand, is less scattered by
soft tissues and it has been in use for imaging in biomedical ultrasound systems. Combination of
the contrast sensitive property of light and good localization of ultrasound provides a challenging
technique to reconstuct images of thicker biological tissues deep inside the body non-invasively.
The US modulated optical signals which traverse the tissue are detected by using a CCD camera
as detector array and the pixel map formed on the CCD is used to characterise the embedded
inhomogeneity. The use of CCD camera improves the signal-noise-ratio (SNR) by averaging the
signals from all of the CCD pixels. The conventional filtered backprojection algorithm is used for
reconstruction. The pixel map is a measure of the projection data. A sequence of two to four images
are captured on CCD camera with phase of US modulation signal shifted by 0 ◦ , 90 ◦ , 180 ◦ and 270 ◦
w.r.t. the signal of the laser source. From these images, the modulation depth (ac/dc) and the
correlation co-efficient of the signals which are the signatures of the pathological changes can be
extracted. It is possible to reconstruct 2-D or 3-D images of a tissue object parameters using this
method. For pre-clinical study of validity of the system, an inanimate object (phantom) is used as
sample tissues. The phantom used is made of poly vinyl alcohol (PVA) and its mechanical, optical,
and acoustic properties are tailored by subjecting an acquous solution of PVA stock and water to a
suitable number of freeze-thaw cycles and by varying the degree of hydrolysis in the PVA stock.
Keywords: Insonified, Tagged, Inhomogeneity, Backprojection

A filament in an active medium:
buckling, stiffening and negative dissipation
Norio Kikuchi 1 , Allen Ehrlicher 2 , Daniel Koch 2 , Josef A. K¨as 2 , Sriram Ramaswamy 1 ,
and Madan Rao 3,4
1 Centre for Condensed Matter Theory, Department of Physics,
Indian Institute of Science, Bangalore 560 012, India
2 Institute of Soft Matter Physics, Linn´estraße 5, 04103 Leipzig, Germany
3 Raman Research Institute, C.V. Raman Avenue, Bangalore 560 080, India
4 National Centre for Biological Sciences (TIFR), Bellary Road, Bangalore 560 065,
India
We present a generic theory for the dynamics of a stiff filament in an active
medium with orientational correlations, such as a microtubule in contractile
actin. In sharp contrast to the case of a passive medium, we find the filament
can stiffen, and possibly oscillate, or buckle, depending on the contractile or
tensile nature of the activity and the filament-medium anchoring interaction.
We present experiments on the behaviour of microtubules in the growth cone
of a neuron, which provide evidence for these apparently opposing
behaviours. We also demonstrate a strong violation of the
fluctuation-dissipation (FD) relation in the effective dynamics of the filament,
including a negative FD ratio. Our theory also applies to the dynamics of
axons and auditory hair cells. Detailed tests of our predictions can be made
using a single filament in actomyosin extracts or bacterial suspensions.

POSTER
ABSTRACTS

Enhancement of sensitivity of detection of Kerr rotation by time
averaging
Arjun Joshua and V. Venkataraman
Abstract
Experiments in spintronics necessarily involve the detection of spin polarization. The sensitivity
of this detection becomes an important factor to consider when extending the low temperature
studies on semiconductor spintronic devices to room temperature, where the spin signal is weaker.
In pump-probe experiments which optically inject and detect spins, the sensitivity is often improved
by using a photoelastic modulator (PEM) for lock-in detection. However, spurious signals can arise
if diode lasers are used as optical sources in such experiments, along with a PEM. In this work,
we eliminated the spurious electromagnetic coupling of the PEM onto the probe diode laser, by
the double modulation technique. We also developed a test for spurious modulated interference
in the pump-probe signal, due to the PEM. Besides, an order of magnitude enhancement in the
sensitivity of detection of spin polarization by Kerr rotation, to 3 × 10 −8 rad, was obtained by
using the concept of Allan variance to optimally average the time series data over a period of 416
s. With these improvements, we are able to experimentally demonstrate at room temperature,
photoinduced steady-state spin polarization in bulk GaAs.
Thus, the advances reported here
facilitate the use of diode lasers with a PEM for sensitive pump-probe experiments. They also
constitute a step towards detection of spin-injection in Si at room temperature.

Reentrant phase behavior of a mixed surfactant system with
strongly binding counter-ions
Vikram Rathee 1 , Sajal Kumar Ghosh 2 , Rema Krishnaswamy 1 ,
V. A. Raghunathan 2 and A. K. Sood 1
1 Department of Physics, Indian Institute of Science, Bangalore
2 Raman Research Institute, Bangalore
The role of strongly binding counter ion in a mixed surfactant system consisting of
oppositely charged amphiphiles, is to decrease the spontaneous curvature of the
micellar aggregates giving rise to a change in their morphology from
Spheres Rods Disks Vesicles , on varying the surfactant composition.
Hence a rich phase behavior is observed in the concentrated micellar solutions of such
systems with a variety of liquid crystalline phases. We will present our recent studies on
the microstructure and dynamics of micellar solutions consisting of an anionic surfactant
sodium dodecyl sulphate (SDS) and a strongly binding counter ion paratoluene
hydrochloride (PTHC).
Small angle x-ray scattering studies reveal a novel route from hexagonal to lamellar
phase through a reentrant phase transition rod like Nematic Isotropic disk
like nematic, on varying α= [PTHC]/[SDS], molar ratio at a fixed surfactant
concentration (1). We will present our studies on SDS+PTHC system with higher
surfactant concentration. A distinct viscoelastic and flow behavior is observed for the two
nematic phases. The results are analyzed in conjunction with the observation from
polarizing microscope and x-ray scattering measurements.
(1) S.K.Ghosh, Ph.D. Thesis; Raman Research Institute, Bangalore (unpublished).

Structural, magnetic and EMR studies of CaMnO 3 nanoparticles
Geetanjali, D. Banerjee and S V Bhat
Calcium manganite, CaMnO 3 is the end member of the much studied doped rare earth pervoskite
RE 1-x Ca x MnO 3 (x=1) and is a G-type antiferromagnetic insulator, with a Neel temperature of
120 K. Recently we have shown that [1] many rare earth manganites loose their antiferromagnetic
ground state and become ferromagnetic when prepared in nano scale (nanoparticles and nanowires).
In this work, we investigate the behavior of CaMnO 3 nanoparticles.
Sol-gel method was used to prepare the calcium manganite nanoparticles (D~50 nm). XRD, TEM
and SEM were used to characterize the sample. X-band EMR studies were carried out between
room temperature and 4 K. At room temperature, a relatively narrow (ΔH pp ≈ 900 Oe) and strong
signal was observed in contrast with the broad (ΔH pp ≈ 1300 Oe), weak signal observed in the bulk
CaMnO 3 [2]. The line-width shows a further reduction around 270 K indicating a possible
ferromagnetic transition and a sharp increase around 120 K characteristic of an antiferromagnetic
transition. The details of ac-susceptibility measurements and the analysis of EMR parameters will
be presented in an attempt to understand the magnetism in nanoparticles of CaMnO 3 .
References:
[1] S.S.Rao, K.N. Anuradha, S.Sarangi, and S.V. Bhat; APL., 87, 182503 (2005)
S.S.Rao, S. Tripathi, D.Pandey and S.V. Bhat, Phys. Rev. B 74, 144416 (2006)
[2] S.B. Oseroff, M. Torikachvili, J. Singley, S. Ali, S.W. Cheong, S.Schultz, Phys. Rev. B 53,
6521 (1996)
Acknowledgments:
The authors would like to thank M.M. Borgohain, K.G. Padmalekha and K.S. Bhagyashree for help
in experiments.
Dr. P.S. Anil Kumar’s help in ac-susceptibility measurements is gratefully acknowledged.

Magnetic and Magnetotransport studies of ZnO films with and without
intrinsic magnetic moment
Sayak Ghoshal and P.S.Anil Kumar
Department of Physics, Indian Institute of Science, Bangalore-560012, INDIA
Transition metal doped ZnO was perceived to be an important material in view of the
applications in Spintronic devices. Recently, we have shown that under suitable conditions of
preparation, pure ZnO also can exhibit intrinsic magnetic moment and we were able to tune this
moment by tuning the oxygen content in the pure ZnO films. We have also shown that this
intrinsic moment is suppressed by an order of magnitude by doping with transition metal, in our
case Cobalt. In addition, the magnetic properties of the bulk Co doped ZnO is also process
dependent. Transport studies on the pure ZnO films reveal the correlation between the carrier
concentration and the magnetic property of these films, which in turn helps us to exclude the
extrinsic origin of the moment. We observed negative magnetoresistance (MR) for the ZnO films
with higher conductivity and with intrinsic moment and positive MR for the less conducting
diamagnetic ZnO films at 4.6K. For the doped sample we observe competition between the
positive and negative MR and their behavior at different temperatures and fields. In this
presentation, magnetic and magneto-transport properties of pure as well as Co doped ZnO films
will be presented.

Ginzburg Landau Theory for Cuprate Superconductivity
Sumilan Banerjee, Chandan Dasgupta, and T. V. Ramakrishnan ∗
Dept. of Physics, Indian Institute of Science,
Bangalore 560012. ∗ Also Banaras Hindu University, Varanasi 221005, India.
Abstract
We propose and develop the consequences of a theory in which the free energy F of a cuprate is
expressed as a functional of the complex nearest neighbour spin singlet bond pair order parameter
∆ ij exp (iφ ij ). F is a sum of two terms ∑ m (a∆2 m +b∆4 m ), and F 1 = c ∑ mn ∆ mn cos (φ m − φ n ); here
m is the site corresponding to ij on the dual lattice (also square) and m,n are nearest neighbours.
The doping x and temperature T dependences of a,b and c are rationalized ( eg, c ∝ x for small x).
The pseudogap ( due to incoherent bond pairs) and the parabolic x dependence of T c ( AF ordering
of the 2d-XY spin ∆ m exp (iφ m ) leading to d wave superconductivity) are described. The observed
C v (T) behaviour is shown to be due to order parameter fluctuations. Detailed calculations of the
vortex structure show a crossover from a Josephson like to a BCS like form with increasing doping,
mirroring a similar change in superconductivity.
1

Non Equilibrium noise in electrophoresis: the micro-ion wind
Suropriya Saha and Sriram Ramaswamy
We have obtained the extended nonequilibrium Langevin eqs for a single colloidal particle
in externally applied electric field. The eq. for the system has been obtained by Squires
who has assumed that only source of noise is thermal and satisfies Fluctuation-dissipation.
We have looked into the manner in which the fluctuations of the counter-ion concentration
lead, in the presence of an electric field to additional sources of noise in the colloid motion.
We have shown that the particle shows enhanced brownian motion (the ‘extra-noise’ being
proportional to field strength), i.e. systems are in steady non-equillibrium states. We have
studied two systems- SysI: A neutrally buoyant particle drifting uniformly under the field
in an unbounded fluid; SysII: A particle with density higher than the fluid, stably levitated
by the balance between gravity sedimenting it towards a wall and the electric field driving
it away from the wall. A qualitative measure of the extra-noise has been obtained for the
two cases. In the first case the noise is found to be comparable or two to three orders of
magnitude more than the thermal noise. In the second case the noise is found to be at least
comparable to the thermal noise. In both cases the extra noise is anisotropic- strength in
the electric field direction is nearly an order of magnitude more than that in the transverse
plane. An effective temperature (T eff ) is defined as the ratio ωS(ω) , which would be the
2Imχ(ω)
temperature in a thermal equilibrium system. T eff is obtained as a function of frequency
‘ω’ and is shown that T eff has strong ‘ω’ dependence; T eff(ω=0)
changes by a factor of 2 as ω
T
changes from 0 to 5.5Dκ 2 (D = diffusivity of the micro-ion s, κ −1 = debye screening length).
Nonequilibrium effects are clearly very significant in these systems.
Abstarct for Poster
1

Magnetic Anisotropy in Epitaxial Fe/MgO films grown by Pulsed
Laser Deposition
Sakshath. S. and P. S. Anil Kumar
Department of Physics, Indian Institute of Science, Bangalore 560012
Email: sakshath@physics.iisc.ernet.in
Abstract
We report the observation of uniaxial in-plane magnetic anisotropy using MOKE
studies on the top ferromagnetic layer of the Fe/MgO/Fe single crystalline Magnetic
tunnel junctions grown epitaxially on GaAs(100) substrates. Squid measurements show
that independent magnetic switching of the ferromagnetic layers is present at
sufficiently thick MgO layers.

Observation of the exchange spring behavior in hard-soft- ferrite nanocomposite
Debangsu Roy a , and P.S. Anil Kumar a*
a Department of Physics, Indian Institute of Science, Bangalore, 560012, India
Bangalore, 560012, India
Nanocomposite of hard and soft ferrite are prepared by the mixing of the individual
ferrite components at appropriate ratio and subsequent heat treatment. Initially the
microstructure of the individual phases is controlled by suitable processing. We have
observed the exchange spring behavior in the soft-hard ferrite composite for the first time
by tailoring the particle size of the individual phases and by suitable thermal treatment of
the composite. It is found that the exchange interaction dominates over the dipolar
interaction for smaller particle sizes of the soft ferrite. The magnetization of the
composite showed hysteresis loop that is characteristic of the exchange spring system.
With the following method of preparation we were successful enough to get an
enhancement in the Fe3O4 and BaCa2Fe16O27 nanocomposite. An enhancement of
(BH) max of ~13% for a particular mixture compared to the parent hard Ferrite. The
presence of the exchange interaction between the hard and the soft grains was confirmed
by the Henkel plot.

Probing the local stress in Graphene by Raman Spectroscopy
Biswanath Chakraborty, Anindya Das and A.K. Sood
Department of Physics, Indian Institute of Science , Bangalore - 560012,
India
We observe the strain induced softening of G and 2D Raman mode of monolayer
graphene, on Si/SiO 2 . The strain in the graphene flake is largely due to the fabrication
process. During mechanical exfoliation, the graphene layer is stretched as a result of
friction between the HOPG adhered to scotch tape and the oxide surface. We show a
softening up to ~ 32 cm -1 for G peak along with a 2D softening of ~ 80 cm -1 . Both these
modes exhibit splitting into two peaks, which evolve as we vary the incident polarization
direction. This evolution serves as an easy method to determine the local stress axis along
the flake. We also report a non uniform distribution of strain on the graphene sample. A
tensile strain of ~0.4% is reported here.

Electrical detection of spin polarized electrons in semiconductors
using a radio-frequency pick-up coil
Chinkhanlun Guite and V. Venkataraman
Department of Physics, IISc Bangalore
We present here preliminary results from an experiment which involves the measurement of
electronic spin polarization in bulk semiconductors using electromagnetic induction. The
main idea is to excite the electrons from the valence band to the conduction band using a
circularly polarized laser. Due to the strong spin-orbit coupling in the valence band, a part of
the angular momentum of the circularly polarized light is transferred to the electron which
allows the excited electron to be spin polarized to certain degree of efficiency, for e.g. 50%
for GaAs. The spin of the excited electron decays with a lifetime of about 50 ps at 300 K. In
steady state, for a pump intensity of about 200mW at 808nm, a spin polarized density of ~10 9
cm -3 can be achieved in GaAs. The weak magnetization generated by this population can be
detected by sensitive modulation techniques.
The laser light was phase modulated using an electro-optic modulator from left to right
circular polarization at a high frequency of 2.5 MHz. This creates an alternating spin
polarization in the sample, which generates varying magnetic field at the frequency of the
modulator. Using a sensitive inductive pick-up coil with a Q~40 at 2.5MHz and an RF Lockin
Amplifier, the induced voltage can be detected and studied. We have measured a signal of
~10nV in our experimental setup against an expected signal of ~2nV. We are currently
involved in eliminating the spurious intensity modulation background, which is ~5-10 times
larger than the signal, by suitably choosing the phase-modulation scheme. We believe this
measurement technique will give an insight into the behavior of electronic spins inside GaAs
and can be extended to other materials, particularly indirect semiconductors such as Ge.

Polymer Addtives in Decaying Two-Dimensional Turbulence
Anupam Gupta, Prasad Perlekar, and Rahul Pandit
Centre for Condensed Matter Theory,
Department of Physics, Indian Institute of Science,
Bangalore 560012, INDIA
We present direct numerical simulations of decaying, two-dimensional isotropic turbulence with
polymer additives. We find that, on the addition of polymers to the turbulent fluid, the enstrophydissipation
rate reduces. This is the two-dimensional analogue of energy-dissipation-rate reduction
in three-dimensional turbulence. We relate the reduction of the enstrophy-dissipation rate to changes
in the fluid energy spectrum, in the presence of polymers, especially at small length scales.

Numerical study of a glass forming liquid in two dimensions to test the dimension
dependence of the Adam-Gibbs relation
Smarajit Karmakar 1 , ∗ Chandan Dasgupta 1,2, , † and Srikanth Sastry 2,‡
1 Centre for Condensed Matter Theory, Department of Physics, Indian Institute of Science, Bangalore, India
2 Condensed Matter Theory Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India.
In a recent study [1], we confirmed the existence of a dynamic correlation length that grows as the liquid is
supercooled, by performing a detailed finite-size scaling analysis of dynamic heterogeneity in a model glass-forming
liquid. The observed behaviour of this correlation length as a function of temperature is qualitatively consistent with
recent predictions of inhomogeneous mode coupling theory. However, our study also showed that it is necessary to
take into account properties of the underlying potential energy landscape (in particular, the configurational entropy)
to understand the dynamics of supercooled liquids even above the dynamic transition temperature of mode coupling
theory. Contrary to expectations, we found that the empirical Adam-Gibbs relation [2] between the relaxation
time and the configurational entropy describes our simulation results very well. Motivated by this observation, we
have examined whether the same Adam-Gibbs relation also holds good in any arbitrary dimension. We have tried
to determine whether the Adam-Gibbs relation has any dimension dependence by performing molecular dynamics
simulations of the Kob-Anderson binary mixture [5] in two dimensions. This question arises partly because of the
recent success of the Random First Order Transition Theory (RFOT) [3, 4] where configurational entropy plays
a major role, leading to a dimension dependent Adam-Gibbs-type relation[2]. We have also performed a detailed
finite-size scaling analysis of a four-point density-density correlation function [6] to extract the underlying correlation
length and calculated the configurational entropy to test whether one can explain the results using RFOT. We found
that indeed the Adam-Gibbs relation has dimension dependence, but our results are not fully consistent with the
predictions of either mode coupling theory or RFOT.
[1] Growing length and time scales in glass forming liquids - Smarajit Karmakar, Chandan Dasgupta, and Srikanth Sastry,
http://arxiv.org/abs/0805.3104
[2] Adam, G and Gibbs, J H (1965),J. Chem. Phys. 43:139–146.
[3] T. R. Kirkpatrick and P. G. Wolynes, Physical Review A. 35, 3072 (1987)
[4] T. R. Kirkpatrick and D. Thirumalai, Physical Review A. 40, 1045 (1989)
[5] Kob, W and Andersen, H C (1995), Phys. Rev. E 51:4626–4641.
[6] C Dasgupta, A V Indrani, S Ramaswamy and M K Phani, Europhys. Lett. 15, 307(1991)
∗ Electronic address: smarajit@physics.iisc.ernet.in
† Electronic address: cdgupta@physics.iisc.ernet.in
‡ Electronic address: sastry@jncasr.ac.in

Compositional dependence of the optical changes in (As 2 S 3 ) 1-x Sb x
chalcogenide film.
Ramakanta Naik,R.Ganesan,K.S.Sangunni.
Department of Physics, Indian Institute of Science, Bangalore, 560012,India.
Arsenic trisulfide (As 2 S 3 ) is the most studied chalcogenide glass and deserves applications
in infrared optics and optical coatings because of its excellent IR transmission, large glass
forming tendency, and resistance to moisture and chemicals. Studies on thin films of Sb 2 S 3
are attracting wide attention, for its special applications as a target material for television
cameras, microwave devices, switching devices and various opto electronic devices. Even
though As and Sb belongs to the same group of the periodic table, As 2 S 3 and Sb 2 S 3 do not
display the same glass forming tendency. Glassy Sb 2 S 3 is very difficult to form and its
preparation requires high cooling rates. However, addition of As 2 S 3 to Sb 2 S 3 enhances
greatly the glass forming ability of the later and glasses in the mixed As-Sb-S system can
be formed. Recently we prepared the ternary As-S-Sb chalcogenide glass composition
(As 2 S 3 ) 1-x Sb x by keeping As/S ratio same with 2%,7%,10% and 15% of the Sb content.
The purpose of the work is two fold; first to study the local glass structure as a function of
composition and second to explore the possibility of mixed As-S-Sb bridges. A number of
works exist which trace the influence of composition and preparation conditions of the
films on the physiochemical properties. These glasses are sensitive to the absorption of
electromagnetic radiation and show a variety of photo induced effects as a result of
illumination. These changes are accompanied by changes in the optical constants, i.e.,
changes in the optical band gap, refractive index and optical absorption coefficient. These
light-induced changes are favoured in chalcogenide glasses due to their structural
flexibility (low coordination of chalcogens) and also due to their high-lying lone-pair p
states in their valence bands. Annealing of chalcogenide glasses can affect the
photoinduced changes, in particular irreversible effects occur in as-deposited films, while
reversible effects occur in well-annealed films as well as bulk glasses. Changes in local
atomic structure are observed on illumination with light having photon energy near the
optical band gap of the chalcogenide. The film composition was checked by EDAX. The
compositional dependence of the (As 2 S 3 ) 1-x Sb x films were studied through FTIR, XPS and
Raman experiments. Addition of Sb results in the increase of density of the bulk (As 2 S 3 ) 1-x
Sb x alloy. The optical band gap of the (As 2 S 3 ) 1-x Sb x films decreases while the width of
localized states increases with the increase in Sb content. The peak shift and intensity
variation of the core level spectra were resulted due to the addition of Sb. It can be
suggested that the photo and thermally induced changes are caused by chemical bond
redistribution,according to the equation
2M-S=M-M+S-S (1)
Where M stands for As or Sb, S is for sulfer and dash denotes a chemical bond. The
equilibrium of Eq. (1) can be moved in both directions, depending on the initial state of
the film and the conditions of light exposure or annealing. Photo and thermally induced
changes can be assigned to chemical bond redistribution.Bleaching of the asprepared film
due to annealing is assigned to an increase of heteropolar bond density. Photodarkening
of the illuminated film and annealed illuminated film is due to the increase in homo polar
bond density.

Measurement of Heteronuclear dipolar couplings-
A systematic study of cross polarization dynamics for
Separated Local Field (SLF) experiments
Nitin P. Lobo a and K.V. Ramanathan b
a Department of Physics and b NMR Research Centre
Indian Institute of Science, Bangalore-560012
Separated Local Field (SLF) spectroscopy based on the transient
oscillations observed during cross polarization represents a class of two
dimensional solid state NMR experiments in which the coherent transfer of
energy between dipolar coupled spin systems provides a means of resolving
heteronuclear dipolar couplings on the basis of chemical shifts and
characterizing them. It has become one of the important methods of
structural elucidation of oriented molecules. Nematic liquid crystals, which
orient in magnetic field have been extensively studied by this technique. In
this method spin evolution during polarization transfer gives rise to the
dipolar cross peaks, which for a two spin system can be understood to arise
from evolution under mutually commuting zero and double- quantum
subspaces. Under the conditions of exact Hartman-Hahn match, the
evolution in the zero-quantum sub space alone contributes to the dipolar
cross peak while the evolution in the double-quantum sub-space contributes
only to the axial-peak. Increasing the cross peak intensity enhances the
sensitivity of the experiment, while suppression of the axial-peak enables
resolution of cross-peaks arising from small dipolar couplings. This requires
that the initial density matrix is essentially of zero-quantum in nature which
can, for example, be achieved by Polarization Inversion (PI). Subsequently,
the dipolar oscillations are monitored with the removal of the homonuclear
dipolar couplings by a suitable decoupling scheme. Experiments on simple
oriented systems has been carried out to estimate the relative cross-peak to
axial-peak intensities in 2D-SLF experiments based on the dipolar oscillations
during cross polarization. Along with CP pulse sequence other pulse
sequences namely CP with Polarization Inversion (PI-CP), another novel
variation of the standard CP experiment i.e. Equilibrium X-nuclearpolarization
enhanced cross-polarization (EXE-CP) and PISEMA experiment
have been considered. In combination with Frequency Switched Lee-
Goldburg (FSLG) homonuclear decoupling sequences, experiments on the
oriented liquid crystalline samples carried out and the performance of the
pulse schemes compared. Since Dipolar couplings provide useful structural
and dynamics information the present study is aimed at optimizing and
improving methods used for the measurement of heteronuclear dipolar
couplings for static oriented samples using solid state NMR methods.

Detection of microcantilever deflection using electron transport measurements
S.M. Mohanasundaram and Arindam Ghosh
Department of Physics, IISc
Abstract:
Using Silicon bulk micromachining technique, we have fabricated Silicon dioxide microcantilevers.
On top of it, we have deposited and patterned Gold thin films using lift-off
process. When we apply a force on the micro-cantilever, it bends and applies an elastic
strain on the metal film. For our initial experiments, force is applied by using the surface
tension of an evaporating liquid (propan-2-ol). Electrical resistance is measured during
the process. We have found that the mechanical strain clearly translates into a change in
the electrical resistance. We are also planning to measure the resistance fluctuations as
function of mechanical strain. This kind of micro-cantilevers can be used for applications
such as Atomic Force Microscopy (AFM), bio-molecular sensing, etc.

A fluctuation-based probe to criticality in structural transitions
Chandni U and Arindam Ghosh
Department of Physics, Indian Institute of Science, Bangalore- 12.
Many natural phenomena, extending from geophysics, biology to material science, involve
slowly driven dissipative systems that are far from thermal equilibrium. The universal critical
dynamics in these systems defines a class of athermal phase transitions that are triggered only
by an external field that act as the tuning parameter and to which the systems respond through
scale‐free avalanches in physical observables. In spite of decades of research, the relevance of
the tuning parameter in this scale‐invariant dynamics at criticality is still an open question.
Experiments are inconclusive whether these systems self organize to the critical state over a
broad range of external field, or if there exists a unique critical point that is smudged by a wide
critical zone as postulated by the concept of ‘plain‐old criticality’. Here, through experimental
determination of time dependent avalanches, or noise, in electrical resistivity during
temperature‐driven martensite transformation in thin nickel‐titanium films, we demonstrate
that higher order statistics of avalanches can serve as an excellent kinetic detector of criticality
in continuously driven non‐equilibrium systems. We show, for the first time, the existence of a
singular `global instability' or divergence of the correlation length as a function of temperature
in martensite transition indicating, (i) mapping of non‐equilibrium first order phase transition
and equilibrium critical phenomena, and (ii) conventional nature of critical behavior, even
though many previous experimental results as well as theoretical models predict a selforganized
criticality in such systems. These results not only establish an independent
experimental probe to critical phenomena in a wide variety of complex natural systems, but
perhaps also call for a re‐evaluation of existing experimental data in various cases.
References:
1. "Signature of martensitic transformation on conductivity noise in thin films of NiTi shape
memory alloys", Chandni U., Arindam Ghosh, H. S. Vijaya and S. Mohan, Applied Physics
Letters 92, 112110 (2008). (Also in arXiv:0811.0101 (2008))
2. “Criticality of tuning in athermal phase transitions”, U. Chandni, Arindam Ghosh, H. S.
Vijaya and S. Mohan, arXiv:0811.0102 (2008).

Temperature dependent photoluminescence study in Hg 1-x Cd x Te
(x~0.8) nano and microcrystals
Jayakrishna Khatei and K.S.R. Koteswara Rao
Abstract
Hg 1-x Cd x Te (MCT) nanoparticles have been prepared by solvothermal method
which is a facile, low-cost, solution phase approach to the large scale preparation of MCT
at 180 o C. Different compositions of MCT (x~0.1, 0.3, 0.4, 0.5 & 0.8) have been prepared
by varying the proportion of Hg and Cd. EDAX result revealed that the compositions are
very much close to the intended one. The photoluminescence (PL) measurements of
nanocrystalline Hg 1-x Cd x Te (x~0.1, 0.3, 0.4, 0.5 & 0.8) have been performed at room
temperature as well as low temperature. The temperature dependent PL characterization
has been done over the temperature range 10-300 K on higher composition Hg 1-x Cd x Te
(x~0.8) nanocrystals. The detailed characteristics of the PL emission which shows a
broad emission from 0.6eV to 1eV consisting of 5 prominent peaks (0.92, 0.76, 0.68, 0.61
and 0.57eV) and the peak intensity at different temperature were studied. With increasing
temperature, these peaks show different temperature dependences. The intensity of most
of the peaks increases with temperature from 10 K to 50 K and then the intensity
decreases with increase in the temperature. The position of the emission peaks remains
constant with change in temperature. These anomalous intensity behaviors of the PL
spectra are explained on the basis of defect levels.
* The results will be presented as poster.

The Dependance of Spiral-Wave Dynamics on Inhomogeneities in the TNNP Model of
Cardiac Tissue
Alok Ranjan Nayak 1 , T.K. Shajahan 2 , and Rahul Pandit 1
1 Centre for Condensed Matter Theory,
Department of Physics, Indian Institute of Science,
Bangalore 560012, INDIA
and
2 Indian Institute of Science Education and Research (IISER),
Thiruvananthapuram 695016, INDIA
Regular electrical activation waves in cardiac tissue lead to the rhythmic contraction and expansion
of the heart that ensures blood supply to the whole body. Irregularities in the propagation
of these activation waves can result in cardiac arrhythmias, like ventricular tachycardia (VT) and
ventricular fibrillation (VF), which are major causes of death in the industrialised world. Indeed
there is growing consensus that spiral or scroll waves of electrical activation in cardiac tissue are
associated with VT, whereas, when these waves break to yield spiral- or scroll-wave turbulence,
VT develops into life-threatening VF: in the absence of medical intervention, this makes the heart
incapable of pumping blood and a patient dies in roughly two-and-a-half minutes after the initiation
of VF. Thus studies of spiral- and scroll-wave dynamics in cardiac tissue pose important challenges
for in vivo and in vitro experimental studies and for in silico numerical studies of mathematical
models for cardiac tissue.
We present a detailed and systematic study of spiral-wave turbulence in a mathematical model
for ventricular myocytes proposed recently by ten Tusscher et al [1] In particular, we use extensive
numerical simulations [2] to elucidate the interaction of spiral-wave in it with conduction and ionic
inhomogeneities that occur commonly in cardiac tissue. We also examine a control scheme that has
been suggested for the control of spiral turbulence, via low-amplitude current pulses, in this model.
[1] ten Tusscher, K.H.W.J., Noble, D., Noble, P.J., Panfilov, A.V. A model for human ventricular tissue.Am. J. Physiol. Heart
Circ. Physiol. 286, H1573−H1589, 2004.
[2] T.K. Shajahan, Alok Ranjan Nayak, and Rahul Pandit. Spiral-Wave Turbulence and its Control in the Presence of Inhomogeneities
in Four Mathematical Models of Cardiac Tissue. Submitted for publication, 2008.

Motion of falling spheres and rising bubbles in a viscoelastic gel:
spontaneous oscillations and bursting
Nitin Kumar 1 , Sayantan Majumdar 1 , Aditya Sood 2 , Rama Govindarajan 3 , Sriram Ramaswamy 1 and A.K. Sood 1
1
Department of Physics, Indian Institute of Science, Bangalore-560 012, India
2 Department of Materials and Metallurgical Engineering, Indian Institute of Technology, Kanpur-208 016, India
3 Engineering Mechanics Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore-560 064, India
Abstract
The motion of a spherical ball falling under gravity through a simple Newtonian fluid is governed by the
well-known Stokes’ law where the ball attains a steady terminal velocity after a certain time when the net
force on the ball becomes zero. However, in non-Newtonian fluids, the velocity of the ball does not
achieve a steady state and shows large fluctuations [1] .
We will report our recent experiments done in surfactant CTAT in water, which forms a viscoelastic
wormlike micellar gel. We show experimentally that a ball falling in the viscoelastic gel undergoes a
transition from a steady state velocity to oscillatory behaviour as the weight of the ball is increased. The
oscillations in velocity of the ball are non-sinusoidal, consisting of high-frequency bursts occurring
periodically at intervals long compared to the period within the bursts. We offer a simple theoretical
model based on the interplay of the mobility tensor of the particle and the orientational order parameter of
the micelle solution. For the case of bubbles, the situation is interesting as both shape and size can vary [2] .
We show that an air bubble rising in the viscoelastic gel shows a discontinuous jump in the velocity at a
critical volume (V c ) jump , of the bubble, followed by a drastic change in its shape from a "teardrop" to
almost spherical. We also observe shape oscillations for bigger bubbles with the tail swapping in and out
periodically.
References:
[1] A. Jayaraman and A. Belmonte, Phys. Rev. E (67), 065301(R) (2003)
[2] Nestor Z. Handzy and Andrew Belmonte, Phys. Rev. Lett. 92, 124501 (2004)

Negative viscosity fluctuations and their universality in a driven repulsive colloidal
glass
Sayantan Majumdar and A.K. Sood
Department of Physics, Indian Institute of Science, Bangalore 560012, India
Abstract
There are a lot of recent interests in the statistical properties of non-equilibrium fluctuations in
driven jammed systems. Recently proposed Fluctuation Relations (FR) [1] predict the symmetry
properties of the Probability Distribution Functions (PDF) of these fluctuations arbitrary far from
equilibrium. Also it has been observed that the PDF of a global measure in a large class of highly
correlated equilibrium and non-equilibrium systems have the same functional form [2].
In this context we have studied the statistical properties of non-equilibrium fluctuations in a
driven repulsive colloidal glass of Laponite. Laponite particles are disk shaped with a diameter of
~30 nm and thickness of ~1 nm. When these particles are suspended in water they acquire more
and more surface charge with time because of gradual ion dissociation. Due to strong long range
electrostatic interaction they can form a colloidal glass even at very low volume fraction (~ 3
wt %). We study the viscosity of 3 wt % Laponite solution in water as a function of time by
applying a constant shear stress on the sample. With time the particles form a highly jammed
state (a colloidal glass). The viscosity (and shear rate) shows large fluctuations including many
negative values. The PDF of these fluctuations can be Gaussian or non-Gaussian depending on
the applied stress but they satisfy the Gallavotti-Cohen Steady State Fluctuation Relation (SSFR)
for both Gaussian and non-trivial case of non-Gaussian PDF. The PDF of global power
fluctuations for very high applied stresses become strongly non-Gaussian and follow exactly the
same Universal functional form predicted in [2]. We attribute this remarkable observation to the
presence of high degree of spatial and temporal correlation in a jammed state.
References
[1] G. Gallavotti and E. D. G. Cohen, Phys. Rev. Lett. 74, 2694 (1995); G. Gallavotti and E. D.
G. Cohen, J.Stat.Phys. 80, 931 (1995).
[2] S. T. Bramwell et al. Nature, vol 396, 10 December 1998; S. T. Bramwell et al. Phys. Rev.
Lett. 84, 3744 (2000).

MAGNETOTRANSPORT STUDIES OF FLOAT ZONE-GROWN Gd 1-x Sr x MnO 3
SINGLE CRYSTAL
Aditya A. Wagh, H.L.Bhat, P. S. Anil Kumar and Suja Elizabeth
Department of Physics, Indian Institute of Science, Bangalore-560012, India
The multiferroic behavior, observed in manganites containing small rare-earth cations,
has attracted considerable attention in recent times because of the interesting physics involved
as well as their high application potential (1). Colossal Magnetoresistance exhibited by mixed
valence perovskites has motivated us to study the effect of strontium substitution in
multiferroic gadolinium manganite crystals. Single crystal of Gd 1-x Sr x MnO 3 (x=0.5) was grown
by Float Zone (FZ) technique. Initially, Gd 1-x Sr x MnO 3 was synthesized by solid state reaction.
Crystals were grown using four mirror optical image furnace with a typical growth rate of 1
mm/hr. Crystallinity was ascertained by X-ray diffraction. Chemical composition was
estimated by ICPAES analysis. Transport properties of grown crystals were studied in the
temperature range 40 to 300 K. Temperature evolution of electrical resistivity of all the crystals
showed semiconducting behaviour as expected (2). Magnetoresistance measurements were
performed by applying a magnetic field perpendicular to the direction of current. Drastic
reduction in the resistivity was observed in the presence of magnetic field. At relatively high
magnetic field a metal-insulator transition was observed and this transition temperature was
field dependent. The temperature and field dependence of the magnetoresistance was also
studied in detail. The magnetization of the samples was measured by vibrating sample
magnetometer in the temperature range 5 to 300 K. Gd 0.5 Sr 0.5 MnO 3 crystal exhibited a
bifurcation in the zero-field cooled (ZFC) and field cooled (FC) plots. The electrical and the
magnetic properties of these crystals will be discussed in detail.
References:
(1) Kadomtseva A. M. et. al. JETP Letters, Vol. 82, No. 9, pp. 590–593 (2005)
(2) Garcia-Landa B. et. al. Journal of Applied Physics, Vol. 83, No.12,7664 (1998)

Conformational modification by conjugation
length and solvent in rigid-rod organic
semiconductor
Paramita Kar Choudhury * , Debjani Bagchi, and Reghu Menon
Department of Physics, Indian Institute of Science, Bangalore 560012, India
The conducting polymer MEH-PPV poly [2-methoxy-5-2 ’ –ethyl-hexyloxy)-1,4-
phenylene vinylene] is an important optoelectronic material for thin film devices, as it
exhibits fluorescence in the visible region of the spectrum. By studying the polymer chain
conformations with small angle X-ray scattering (SAXS), we have explored the factors
such as conjugation length and effect of solvents, which can remarkably alter the
fluorescence and conductivity of MEH-PPV films. The studies reveal that increase in
effective conjugation in organic polymers changes their conformation by making them
more rigid-rod like in the nano-scale regime. At a slightly larger length scale we find
oriented stacking and long range ordering of the worm-like chains even in a very dilute
solution. Aromatic non-polar solvent xylene solvates the backbone leaving the chains
more rigid and stacked, while non-aromatic polar solvent tetrahydrofuran (THF) solvates
the lateral groups and leads to lesser, and more randomly oriented coil structures.

1H-NMR and charge transport in metallic polypyrrole at ultra-low
temperatures and high magnetic fields
K Jugeshwar Singh, G Clark, K P Ramesh and Reghu Menon
The temperature dependence of conductivity, proton spin relaxation time (T1) and
magnetoconductance (MC) in metallic polypyrrole (PPy) doped with PF6. have been
carried out at mK temperatures and high magnetic fields. At T < K both electron.electron
interaction (EEI) and hopping contributes to conductivity. The temperature dependence
of a proton T1 is classified in three regimes: (a) for T 50 K,
relaxation is due to the dipolar interaction modulated by the reorientation of the
symmetric PF6 groups following the Bloembergen, Purcell and Pound (BPP) model. The
data analysis shows that the Korringa ratio is enhanced by an order of magnitude. The
positive and negative MC at T < 250 mK is due to the contributions from weak
localization and Coulomb-correlated hopping transport, respectively. The role of EEI is
observed to be consistent in conductivity, T1 and MC data, especially at T

Resistance noise in electrically biased bilayer graphene
Atindra Nath Pal and Arindam Ghosh
Department of Physics, Indian Institute of Science, Bangalore 560 012, India
Abstract:
The growing interest in bilayer graphene (BLG) is fueled by the ability to control the energy gap
between its valence and conduction bands through external means. We demonstrate that the
low‐frequency resistance fluctuations, or noise, in bilayer graphene is strongly connected to its
band structure, and displays a minimum when the gap between the conduction and valence
band is zero. Using double‐gated bilayer graphene devices we have tuned the zero gap and
charge neutrality points independently, which offers a unique mechanism to investigate the
low‐energy band structure, charge localization and screening properties of bilayer graphene.
We show: (1) the noise to be minimum when band gap (Δ g ) = 0 even if it corresponds to a
nonzero carrier density (n), (2) the evidence of localized states near the band tails even at Δ g =
0, with a mobility edge that strongly depends on the external electric field E, and finally, (3) a
method to directly determine the dielectric properties of BLG in both electron and hole‐doped
regimes.
References:
1. Oostinga, J. B.; Heersche, H. B.; Liu, X; Morpurgo, A. F.; Vandersypen, L. M. K. Nat.
Mater., 7, 151, 2007.
2. T. Ohta, A. Bostwick, T. Seyller, K. Horn, E. Rotenberg, Science 313 (2006) 951.
3. Yu‐Ming Lin and Phaedon Avouris, NANO LETTERS 8 : 2119 DOI 10.1021/nl0802411
2008.
4. E. McCann, Phys. Rev. B 74 (2006) 161403.

Structure and stability of carbon and boron­nitride nanorings
Meghana Dharmik and Prabal Maiti
Center for Condensed Matter Theory,Department of Physics,Indian Institute of Science.
We have studied the structure and stability of Carbon and Boron­Nitride
nanorings using Molecular mechanics calculations.We have used conjugate gradient
method to minimize the nanorings using Dreiding force field to get an estimate of the
critical diameter of the nanoring.Below the critical diameter the ring structure is unstable
with formation of kinks.Above the critical diameter kinks disappear and the ring structure
is stable.The critical diameter of the nanoring strongly depends on the chirality of the
tube and increases with increase in tube diameter .We identify the kink location with the
high strain energy region .Our calculation suggests that for a given chirality Boron –
Nitride nanoring has larger critical diameter than the corresponding Carbon nanoring.
This might be due to the strong coulombic interaction arising due to the polar interaction
between the B and N atoms.

Conductivity noise in strongly correlated systems
R.Koushik and Arindam Ghosh
Department of Physics,
Indian Institute of science, Bangalore- 560012, India
Abstract:
Modulation doped GaAs/AlGaAs heterostructures are ideal candidates to study the
effects of disorder on electron-electron interaction in a systematic manner. In these
systems the strength of the disorder is determined by an undoped AlGaAs spacer, which
separates the charged silicon dopants from the two dimensional electron gas, and can be
tuned to atomic precision in molecular beam epitaxy. Several disorder-stabilized strongly
interacting many-body phases have been predicted in numerous theoretical studies in
these systems, in particular when the effect of interaction is non-perturbative.
Conventional techniques, based on time averaged current-voltage characteristics, are
however often inconclusive in this regard. In this work, we report the measurement of
low-frequency resistivity fluctuations in mesoscopic 2D electron systems in delta-doped
GaAs/AlGaAs heterostructures in the strongly interacting regime. Our measurements at
low temperatures (267 mK) reveals a spectacular increase over six orders of magnitude in
resistivity noise with a decrease in applied bias, which cannot be explained using hopping
(variable-range or nearest-neighbor) conduction mechanisms. Our measurement
technique is quite unique in the sense we have kept the AC bias across the sample
constant at 30uV and varied the DC bias across the sample from -800uV to +800uV. We
attribute the results to the manifestation of a new many-body quantum state of the
electrons that has been recently claimed in the context of metallic transport in 2D.
References:
1. Modulation origin of 1/f noise in two-dimensional hopping, V.Ya.Pokrovskii, A.V.
Savchenko, W.R. Tribe and E.N. Linfield, Phys Rev B 64, 201318 (2001)
2. Onset of glassy dynamics in a Two-Dimensional Electron system in Silicon, Snezana
Bogdanovich and Dragana Popovic, PRL 88, 236401 (2002)
3. Low temperature collapse of electron localization in two dimensions, Matthias
Baenninger, Arindam Ghosh, Michael Pepper, Harvey E.Beere, Ian Farrer, and David
A. Ritchie, PRL 100, 016805 (2008)
4. Conductivity noise in strongly correlated systems, R. Koushik, Baenninger et al.
under preparation

Out-of-Equilibrium Microrheology to Probe Directional
Viscoelastic Properties under Shear
Manas Khan and A. K. Sood
Department of Physics, Indian Institute of Science, Bangalore - 560012, India
Many wormlike micellar systems exhibit appreciable shear thinning due to shear induced
alignment. As the micelles get aligned, introducing directionality in the system, the
viscoelastic properties no longer remain isotropic. An optical tweezers based technique
enables us to probe the out-of-equilibrium rheological properties of CTAT system
simultaneously along two orthogonal directions - parallel to the applied shear, as well as
perpendicular to it. While the displacements of a trapped bead - in response to active drag
force - carry signature of conventional shear thinning, its spontaneous position
fluctuations along the perpendicular direction manifest an orthogonal shear thickening.

Jump reorientation of water molecules confined in narrow carbon
nanotubes
Biswaroop Mukherjee 1,3, , ∗ Prabal K. Maiti 1,∗ , † Chandan Dasgupta 1,3, , ‡ and A. K. Sood 2,§
1 Centre for Condensed Matter Theory, Department of Physics,
Indian Institute of Science, Bangalore 560 012, India
2 Department of Physics, Indian Institute of Science, Bangalore 560 012, India
3 Condensed Matter Theory Unit, Jawaharlal Nehru Centre
for Advanced Scientific Research, Bangalore 560 064, India.
Abstract
We use molecular dynamics (MD) simulations to study the reorientational dynamics of water
molecules confined inside narrow carbon nanotubes immersed in a bath of water. Our simulations
show that the confined water molecules exhibit bistability in their reorientational relaxation,
which proceeds by angular jumps between the two stable states. The energy barrier between these
two states is about 2k B T. These jumps cause the ratio of the timescales of the first and second
order reorientational correlation functions to exceed the value in the diffusive limit. The analytic
solution of a simplified model, which qualitatively explains this “unusual” relaxation, is also
presented. These results will have important implications in understanding proton conduction in
water-filled ion channels.
PACS numbers:
1

∗
Electronic address: biswa@physics.iisc.ernet.in
† Electronic address: maiti@physics.iisc.ernet.in
‡ Electronic address: cdgupta@physics.iisc.ernet.in
§ Electronic address: asood@physics.iisc.ernet.in
2