Laboratoire National des Champs Magnétiques Pulsés CNRS – INSA

Personnel involved:
Nanosciences
Permanent: J-M Broto (E-C), W. Escoffier(E-C), S. George (Tech), M. Goiran (E-C), O. Portugall (IR), B.
Raquet (E-C), G. Rikken (C).
Non permanent: J. Jorge (PhD), A. Kumar (Post-doc) B. Lassagne (PhD), M. Millot (PhD), S. Nanot (PhD), J-M
Poumirol (PhD), N. Ubrig (PhD)
Collaboration: E. Flahaut (CIRIMAT- Tlse), M. Monthioux & Th. Ondarçuhu (CEMES – Tlse), Ch. Vieu
(LAAS), L. Forro (EPFL), S. Roche (CEA), K. Novoselov (Univ Manchester), J Blokland (HFML - Nijmegen),
F. Gonzalez (Univ. Caracas), J. Gonzalez (Univ. Merida) J. Kono, N.Parra-Vasquez & J. Shaver (Rice
University, Houston), S.A. Crooker & C. Mielke (NHMFL, Los Alamos), M. Potemski & P. Plochocka (LCMI,
Grenoble),Ch. Caillier & A. San Miguel (LPMCN- Lyon), J. Gómez Herrero & D. Martínez Martín (Univ. Aut.
de Madrid, Spain), R.J. Nicholas & I.B.Mortimer (University of Oxford).
An important trend in modern sciences is the investigation of individually addressed objects with properties
determined by a nano-sized group of atoms or molecules. There is an increasing demand from the high magnetic
field community to extend single-object measurements up to the highest magnetic fields, to benefit from the
powerful combination of nanosciences and high fields. Indeed, the magnetic length, defined by lB � �eB
(3 nm
at 74T), becomes comparable to typical dimensions of nano-objects, leading to significant changes in their
energy spectrum: the magnetic field drastically lifts the spin and orbital motions of electrons allowing advanced
magneto-spectroscopy experiments.
Our activities in nanophysics are focused on (i) (magneto)-transport properties of individually addressed carbon
nanotubes and exfoliated graphene and graphene nano-ribbons, and (ii) NIR magneto-optical properties of
carbon nanotubes in solution and epitaxial graphene. Note that individual nano-scale samples are usually
extremely delicate to handle and can easily be damaged by the aggressive electrical environment inherent to the
control of the capacitors bank. Specific procedures, shielding and filters are used to safely measure the 60T
magneto-conductance of individual carbon nanotubes as well as graphene.
Carbon nanotube based devices under magnetic field
Carbon nanotubes have already demonstrated their wide potential in nanoelectronics and optoelectronics even if
their large scale integration raises cumbersome issues. The unique electronic structure of a graphene sheet
combined to a tubular confinement leads to remarkable one dimensional charge transport properties in carbon
nanotubes. In a recent past, both theoretical and experimental evidences unveiled the large energy dependence of
the transport regime in individual CNT (from ballistic to diffusive), by playing with the electrochemical potential
level. In our study, we demonstrate that an applied magnetic field, along with a control of the electrostatic
doping, drastically modifies the electronic band structure of a carbon nanotube based transistor [G. Fedorov & al.,
Phys. Rev. Lett. 94, 066801(2005)]. We give evidence of unconventional quantum phenomena like the giant
Aharonov-Bohm modulation of the electronic density of states [B. Lassagne & al. Phys. Rev. Lett 98, 176802
(2007)] or the onset of propagative Landau states in the high magnetic field regime [B. Raquet & al. Phys. Rev.
Lett. 101, 046803 (2008)].
In a parallel configuration (B applied parallel to the tube axis), a quantum flux threading the tube induces a giant
Aharonov-Bohm conductance modulation mediated Schottky barriers which profile is magnetic field dependent
(Fig.1). Recently, we explore the multi-period quantum flux modulation of the conductance in heavily doped and
ballistic MWCNTs controlled by an efficient back-gate voltage [S. Nanot & al, C. R. Physique, in press (2009)].
In the perpendicular configuration, experiencing the Landau states by Hall measurements remains an unsolved
technological challenge. By playing with a carbon nanotube based electronic Fabry-Perot resonator, we have
recently demonstrated that the electronic transmission of the device can be modified by a moderate transverse
magnetic field (35T) – Fig.2. The field dependence of the resonant states of the cavity reveals the onset of the
first landau state at zero energy. New experiments under 60T give experimental evidence of propagative Landau
states in both semiconducting and metallic CNTs. The two-probe conductance in the high magnetic regime
evolves to a unique conducting state, independently of the electrostatic doping. This remarkable phenomenon is
assigned to the onset of propagative electronic states in high fields along with the closing of the energy gap for
semiconducting tubes.
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