Workshop book - Physikzentrum der RWTH Aachen - RWTH Aachen ...
Workshop book - Physikzentrum der RWTH Aachen - RWTH Aachen ...
Workshop book - Physikzentrum der RWTH Aachen - RWTH Aachen ...
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PROGRAM BOOK<br />
International workshop on<br />
Spin-Orbit and Interaction Effects<br />
in Nano-Electronics<br />
<strong>Aachen</strong>, 4-6 February, 2013<br />
Organizers:<br />
Sabine An<strong>der</strong>gassen, Fabian Hassler, Dirk Schuricht, Maarten Wegewijs<br />
1
Table of contents<br />
What comes with this <strong>book</strong>let . . . . . . . . . . . . . . . . . . . . . . . . . 3<br />
Organization and funding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4<br />
Getting to the institute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5<br />
<strong>Workshop</strong> lecture hall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7<br />
Internet access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8<br />
Lunch information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9<br />
Conference dinner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10<br />
Talk program & abstracts . . . . . . . . . . . . . . . . . . . . . . . . . . . 11<br />
Talks Monday February 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . 11<br />
Talks Tuesday February 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . 29<br />
Talks Wednesday February 6 . . . . . . . . . . . . . . . . . . . . . . . . . 47<br />
Poster program & abstracts . . . . . . . . . . . . . . . . . . . . . . . . . 57<br />
Posters Monday February 4 . . . . . . . . . . . . . . . . . . . . . . . . . . 57<br />
Posters Tuesday February 5 . . . . . . . . . . . . . . . . . . . . . . . . . . 71<br />
List of participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85<br />
2
What comes with this <strong>book</strong>let<br />
With this <strong>book</strong>let you should have received<br />
• <strong>Aachen</strong> city plan - Stadtplan <strong>Aachen</strong><br />
• <strong>Aachen</strong> information <strong>book</strong>let - <strong>Aachen</strong> at a glance 2013<br />
which includes restaurant information<br />
If not, please ask at the reception of your hotel !<br />
Please check the workshop website for updates:<br />
http://www.physik.rwth-aachen.de/workshop2013/<br />
• Corrections<br />
• Electronic files of talks and posters<br />
3
Organization and funding<br />
The conference is organized by<br />
• Sabine An<strong>der</strong>gassen (Universität Wien)<br />
• Fabian Hassler (<strong>RWTH</strong> <strong>Aachen</strong> University)<br />
• Dirk Schuricht (<strong>RWTH</strong> <strong>Aachen</strong> University)<br />
• Maarten Wegewijs (Forschungszentrum Jülich)<br />
with administrative support by Julia Heuerz-Sengül, Gabriele Meeßen and<br />
technical support by Uwe Kahlert.<br />
The workshop is funded by<br />
• The European Science Foundation (ESF),through the Research Networking<br />
Programme Quantum Spin Coherence and Electronics<br />
http://www.esf.org/activities/research-networking-programmes/physical-and-engineering-sciences-pesc/currentresearch-networking-programmes/quantum-spin-coherence-andelectronics.html<br />
• DFG Research Unit 912 Coherence and Relaxation Properties of Electron<br />
Spins<br />
http://www.spintransport.de<br />
4
Getting to the institute<br />
(1) If you are staying at Hotel Marschiertor (down town)<br />
Monday:<br />
• Someone from the workshop will pick up a group at the hotel<br />
• To join the group you need to buy bus tickets yourself beforehand<br />
(to avoid ∼ 50 people annoying the bus driver at once):<br />
◦ A ticket machine is located at the central station at the bus<br />
stop and also at the Tabak & Zubehör Shop from T. H. Kleen<br />
on your left when you exit the central station on the side of the<br />
big square.<br />
◦ For the entire workshop you need 6 tickets<br />
2 x single trip (2.50 Euro) + 1x four trips (8.80 Euro) = 13.80 Euro<br />
• Travel time to the institute is about 30 minutes:<br />
The group will leave the hotel strictly at 8.00 to make it in time.<br />
Tuesday-Wednesday:<br />
• Take bus number 3 A or 3 B at central station (Hauptbahnhof )<br />
(Don’t worry that these busses depart in opposite directions.<br />
Also, depending on the departure time, you may need to change bus once)<br />
• Your destination is Campus Melaten<br />
• Exiting the bus, go up the stairs towards the ugly building with yellow<br />
on the roof (<strong>Physikzentrum</strong>) which has 26 written on it in big letters.<br />
• Enter the tower and go to lecture hall 28 D001 (Hörsaal Physik) on<br />
the 1st floor.<br />
5
(2) If you are staying at the <strong>RWTH</strong>-Guesthouse<br />
Travel time to the institute is about 15 minutes on foot.<br />
Monday: particant Fabian Heidrich-Meisner will bring a group to the institue.<br />
The group will leave the guesthouse strictly at 8.15 to make it in time.<br />
Tuesday-Wednesday:<br />
• Exiting the reception of the <strong>RWTH</strong>-Guesthouse, turn left on the<br />
Melatener Strasse and follow it all the way: you will cross an intersection<br />
with Halifaxtrasse and finally continue across a bridge over<br />
the highway (Pariser Ring).<br />
• Descent from the bridge and on go up the stairs to the ugly looking<br />
building with yellow on the roof (<strong>Physikzentrum</strong>). You will see it has<br />
28 written on it in big letters.<br />
• Enter the building and go to lecture hall 28 D001 (Hörsaal Physik) on<br />
the 1st floor.<br />
6
<strong>Workshop</strong> lecture hall<br />
• The workshop talks take place in the main lecture hall,<br />
28D 001 Hörsaal Physik, on the 1st floor<br />
Just follow the signs.<br />
• The poster sessions take place in front of the lecture hall.<br />
7
Internet access<br />
Power: all seats in the lecture hall are equipped with a power outlet.<br />
Wireless internet:<br />
• If you have an eduroam account:<br />
simply log on as usual<br />
• In all other cases, you can make use of a special workshop guest<br />
account.<br />
Simply fire up your browser, and try to go to an arbitrary website. You<br />
will be redirected to the login URL of the <strong>RWTH</strong> computing center<br />
(Rechenzentrum). Log on using:<br />
◦ Login name: see printed version<br />
◦ Password: see printed version<br />
For more advanced technical assistance, please contact:<br />
Uwe Kahlert<br />
Room: 26C 411 (4th floor)<br />
Tel: +49 241 80 27042<br />
uwe@physik.rwth-aachen.de<br />
8
Lunch information<br />
Lunch will be taken at the Mensa Vitae, just 5 minutes away on foot.<br />
Please follow the crowd as we go there at 12.30.<br />
• Vouchers are available each day at the workshop registration desk in<br />
front the lecture hall.<br />
• Coffee after lunch: please note that at the lecture hall there will be<br />
no coffee right after lunch. So if you need coffee, please get it at the<br />
Lavazza counter in the Mensa Vitae.<br />
Lab-tour: on Tuesday you have the possibility of taking a tour through some<br />
of the experimental labs in <strong>Aachen</strong>.<br />
• Please register for this at the workshop registration table in front of<br />
the lecture hall.<br />
• We will serve a few sandwiches for lunch (30 min) and start the tour<br />
with 4 locations immediately afterward:<br />
◦ 13:00 Sub-k scanning tunneling microscope (Morgenstern)<br />
◦ 13:15 Spin-qubits (Bluhm)<br />
◦ 13:30 Quantum-transport graphene nanostructures (Stampfer)<br />
◦ 13:45 Time-resolved optics for spintronics (Beschoten)<br />
◦ 14:00 <strong>Workshop</strong> continues<br />
9
Conference dinner<br />
The conference dinner will take place on<br />
Tuesday evening 19:30<br />
at the Ratskeller, located on the square in the old city center:<br />
To get there,<br />
Ratskeller <strong>Aachen</strong><br />
Markt 40<br />
52062 <strong>Aachen</strong><br />
Tel. 0241-35001<br />
http://www.ratskeller-aachen.de<br />
• Exit the institute using the main access tower 26 (at the side of the<br />
parking lots) and cross the street.<br />
• Take Bus 3B and get out at Ponttor, an old city gate.<br />
• Just walk down the Pontstrasse until you find yourself at the square<br />
After dinner: Many student pubs can be found in the Pontstrasse that you<br />
walked through above....<br />
10
Talks Monday February 4<br />
Talk program & abstracts<br />
Talks Monday February 4<br />
Monday (Feb. 4)<br />
8:45 Opening<br />
9:00 Herre van <strong>der</strong> Zant<br />
Transport through individual magnetic molecules<br />
9:45 San<strong>der</strong> Otte<br />
Atomically assembled quantum spin lattices<br />
10:30 Coffee break<br />
11:00 Ireneusz Weymann<br />
Interplay of the Kondo effect and spin-polarized transport<br />
in magnetic molecules, adatoms, and quantum dots<br />
11:45 Jens Paaske<br />
Fine structure in cotunneling spectroscopy<br />
12:30 Lunch<br />
14:00 Carsten Timm<br />
The master equation for nanoscopic transport:<br />
Spectral analysis, perturbation theory,<br />
and applications to molecular devices<br />
14:45 Jürgen König<br />
Superconducting proximity effect in quantum-dot systems<br />
15:30 Poster session<br />
17:00 Stefan Heinze<br />
Spontaneous atomic-scale magnetic skyrmion lattice<br />
in an ultra-thin film<br />
17:45 Achim Rosch<br />
Magnetic whirls in chiral magnets<br />
18:30<br />
11
Talks Monday February 4<br />
Transport through individual magnetic molecules<br />
Herre van <strong>der</strong> Zant, Kavli Institute of Nanoscience Delft, The Netherlands<br />
By merging the fields of molecular magnetism, molecular electronics and<br />
nanotechnology, we fabricate planar three-terminal nanodevices containing<br />
individual magnetic molecules or nanoparticles. Source and drain electrodes<br />
are made of Au or of (multi-layered) graphene. A third gate electrode allows<br />
the modification of charge transport independently from the source/drain<br />
electrodes. In this way, a spin transistor is built in which the electric current<br />
through the individual magnetic molecule or nanoparticle is sensitive to its<br />
spin properties. The molecular complexes of interest are single-molecule magnets<br />
(SMMs) and spin-crossover compounds. Coulomb blockade is generally<br />
observed but finer details such as Kondo correlations and excited states are<br />
observed at cryogenic temperatures [1]. In a Fe-4 SMM based transistor, we<br />
observe features that confirm the high-spin state and find Kondo behavior,<br />
spin blockade and a zero-field splitting that depends on the redox state; in<br />
the charged state the molecule turns out to be a better magnet. Using an<br />
in-situ sample rotator, direct observation of magnetic anisotropy has been<br />
demonstrated [3]. Recent progress includes transport through a single spincrossover<br />
molecule [4] and the fabrication of a molecular memory device based<br />
on a spin-crossover nanoparticle that operates near room temperature [5].<br />
Interestingly for molecular spintronics, the spin crossover in these devices<br />
can be induced by applying a voltage, showing that its magnetic state is<br />
controllable electrically.<br />
Work supported by FOM and through the EU FP7 program (ELFOS)<br />
[1] H.B. Heersche et al., Rev. Lett. 96 (2006) 206801; E.A. Osorio et al.,<br />
Nano Letters 10 (2010) 105; J.M. Thijssen and H.S.J. van <strong>der</strong> Zant, Phys.<br />
stat. sol. (b) 245 (2008) 1455-1470.<br />
[2] A. Zyazin et al. Nano Letters 10 (2010) 3307.<br />
[3] E. Burzurí, A.S. Zyazin, A. Cornia and H.S.J. van <strong>der</strong> Zant, Phys. Rev.<br />
Lett. 109 (2012) 147203.<br />
[4] V. Meded et al., Phys. Rev. B 83 (2011) 245115.<br />
[5] F. Prins et al. Adv. Mat. 23 (2011) 1545.<br />
12
Talks Monday February 4<br />
Notes<br />
13
Talks Monday February 4<br />
Atomically assembled quantum spin lattices<br />
San<strong>der</strong> Otte, Kavli Institute of Nanoscience Delft, The Netherlands<br />
The physical behavior of lattices consisting of coupled quantum spins is often<br />
hard to predict, even when only few spins are involved. Yet, insight into such<br />
basic lattices can be key towards un<strong>der</strong>standing the fascinating properties of<br />
complex magnetic materials on the macroscopic scale.<br />
In our lab we study small one- and two-dimensional lattices of magnetic<br />
atoms by building them from scratch, literally atom-by-atom, using low temperature<br />
scanning tunneling microscopy. Once built, the atomic structures<br />
can be probed locally using a combination of inelastic electron tunneling<br />
spectroscopy (IETS) and spin-polarized STM.<br />
14
Talks Monday February 4<br />
Notes<br />
15
Talks Monday February 4<br />
Interplay of the Kondo Effect and Spin-Polarized Transport in Magnetic<br />
Molecules, Adatoms, and Quantum Dots<br />
Ireneusz Weymann, Adam Mickiewicz University, Poznań<br />
Theoretical results on the interplay of the Kondo effect and spin-polarized<br />
tunneling in a class of systems exhibiting uniaxial magnetic anisotropy, such<br />
as magnetic molecules, magnetic adatoms, or quantum dots coupled to a<br />
localized magnetic moment will be presented. In particular, the dependence<br />
of the spectral functions and linear conductance on the system’s parameters<br />
will be thoroughly discussed. It will be shown that both the magnetic<br />
anisotropy as well as the exchange coupling between electrons tunneling<br />
through the conducting orbital and magnetic core play an important role<br />
in the formation of the Kondo resonance, leading generally to its suppression.<br />
Specific transport properties of such a system appear also as a nontrivial<br />
behavior of tunnel magneto-resistance. Moreover, the un<strong>der</strong>screened Kondo<br />
effect in spin S=1 magnetic quantum dots will be discussed.<br />
16
Talks Monday February 4<br />
Notes<br />
17
Talks Monday February 4<br />
Fine structure in cotunneling spectroscopy<br />
Jens Paaske, University of Copenhagen, Denmark<br />
Cotunneling through Coulomb blockaded nano-transistors provides an informative<br />
spectroscopy of the system bridging source and drain contacts. In this<br />
talk, I address the question to what extent this transport probe can also tell<br />
us more about the spin-orbit coupling in the dot, tube, wire or molecule un<strong>der</strong><br />
scrutiny. From inelastic cotunneling spectroscopy, one might directly observe<br />
avoided crossings between spin-orbit coupled states, but there are also a<br />
number of more subtle clues to be picked up. What happens to the Kondo<br />
resonances, reflecting the “flippable” degeneracies in the system, what are the<br />
effects on tunneling induced level renormalization, and to what extent have<br />
we already observed some of this spectroscopic fine structure experimentally?<br />
18
Talks Monday February 4<br />
Notes<br />
19
Talks Monday February 4<br />
The master equation for nanoscopic transport: Spectral analysis, perturbation<br />
theory, and applications to molecular devices<br />
Carsten Timm, Technische Universität Dresden, Germany<br />
The master equation is a powerful method for the description of nanostructures<br />
with strong interactions far from equilibrium. Using a master equation<br />
for a molecular device coupled to a vibrational mode as an example, I will<br />
analyze what information can be gained from the spectrum of eigenvalues<br />
of the transition-rate matrix. So far, research has mostly focused on the<br />
stationary state, which is the eigenstate to the (usually unique) vanishing<br />
eigenvalue of this matrix. I will show that its full spectrum and its slowly<br />
decaying eigenstates give useful information on the dynamics and are characteristic<br />
of various regimes, such as the Coulomb and the Franck-Condon<br />
blockade. In practice, the master equation is usually combined with perturbation<br />
theory in the hybridization between the nanostructure and the electronic<br />
leads. I will discuss recent theoretical progress regarding the exact time-convolutionless<br />
(time-local) master equation to all or<strong>der</strong>s in the hybridization.<br />
Finally, I will comment on applications of the master equation to molecular<br />
devices, including the direct comparison with break-junction experiments.<br />
20
Talks Monday February 4<br />
Notes<br />
21
Talks Monday February 4<br />
Superconducting Proximity Effect in Quantum-Dot Systems<br />
Jürgen König, University of Duisburg-Essen, Germany<br />
We theoretically analyze electronic transport through interacting quantum<br />
dots tunnel coupled to normal and superconducting leads. The proximity of<br />
superconducting leads induces superconducting correlations in the quantum<br />
dot which mediate Josephson and Andreev currents through the dot. Based<br />
on a real-time diagrammatic approach formalism, we address non-local<br />
Andreev effects in single- and double dot geometries and discuss the possibility<br />
to induce unconventional (e.g. odd-triplet) pairing amplitudes.<br />
22
Talks Monday February 4<br />
Notes<br />
23
Talks Monday February 4<br />
Spontaneous atomic-scale magnetic skyrmion lattice in an ultra-thin film<br />
Stefan Heinze, University of Kiel, Germany<br />
Skyrmions are topologically protected field configurations with particle-like<br />
properties that play an important role in various fields of science [1]. In<br />
the context of magnetism, they have been predicted to form stable phases<br />
and, recently, experimental evidence for their existence has been found for<br />
bulk materials in a certain range of temperature and magnetic field [2,3]. A<br />
very important ingredient for their occurrence is the Dzyaloshinskii-Moriya<br />
interaction (DMI) which was recently found to be strong also in ultrathin<br />
magnetic films on substrates with large spin-orbit coupling [4]. In these systems<br />
the DMI induces spin-spirals with a unique rotational sense propagating<br />
along one direction of the surface as observed for ultra-thin films [4-6] and<br />
atomic chains [7]. The latter case is a prototypical system in which the<br />
hybridization between the 3d-transition-metal chains (Fe) hybridize strongly<br />
with the heavy 5d-transition-metal substrate (Ir) which leads to a weak<br />
Heisenberg exchange interaction and a dominant DMI. Here, we go a step<br />
beyond and present an atomic-scale magnetic skyrmion lattice for a hexagonal<br />
Fe monolayer on the Ir(111) surface [8]. We develop a spin-model<br />
based on density functional theory that explains the interplay of Heisenberg<br />
exchange, DM interaction and the four-spin exchange as the microscopic<br />
origin of this intriguing magnetic state. Experiments using spin-polarized<br />
scanning tunneling microscopy confirm the skyrmion lattice which is incommensurate<br />
with the un<strong>der</strong>lying atomic lattice.<br />
This work is a collaboration with G. Bihlmayer, S. Blügel, K. von Bergmann,<br />
M. Menzel, A. Kubetzka, J. Brede, and R. Wiesendanger.<br />
[1] T. H. Skyrme, Proc. R. Soc. Lond. Ser. A 260, 127 (1961).<br />
[2] S. Mühlbauer et al., Science 323, 915 (2009).<br />
[3] X. Z. Yu et al., Nature 465, 901 (2010).<br />
[4] M. Bode et al., Nature 447, 190 (2007).<br />
[5] P. Ferriani et al., Phys. Rev. Lett. 101, 027201 (2008).<br />
[6] Y. Yoshida et al., Phys. Rev. Lett. 108, 087205 (2012).<br />
[7] M. Menzel et al., Phys. Rev. Lett. 108, 197204 (2012).<br />
[8] S. Heinze et al., Nature Phys. 7, 713 (2011).<br />
24
Talks Monday February 4<br />
Notes<br />
25
Talks Monday February 4<br />
Magnetic Whirls in Chiral Magnets<br />
Achim Rosch, University of Cologne, Germany<br />
In cubic magnets without inversion symmetry, lattices of magnetic whirls, socalled<br />
skyrmions are stabilized by spin-orbit interactions and thermal fluctuations.<br />
The coupling of these magnetic whirls to electrons can be described<br />
by emergent electric and magnetic field. This coupling is very efficient and<br />
allows to move the skyrmions by ultrasmall current densities. The emergent<br />
fields can be used to detect the presence and motion of the skyrmions. We also<br />
discuss how such skyrmion phases can be created and destroyed by changing<br />
the topology of the magnetic structure.<br />
26
Talks Monday February 4<br />
Notes<br />
27
Talks Tuesday February 5<br />
28
Talks Tuesday February 5<br />
Talks Tuesday February 5<br />
Tuesday (Feb. 5)<br />
9:00 Hartmut Buhmann<br />
Mercury telluride, a topological insulator<br />
9:45 Henrik Johannesson<br />
Electrical control of the Kondo effect in a helical edge liquid<br />
10:30 Coffee break<br />
11:00 Mircea Trif<br />
Resonantly tunable Majorana polariton in a microwave cavity<br />
11:45 Piet Brouwer<br />
Subgap states in Majorana wires<br />
12:30 Lunch + labtour (requires registration)<br />
14:00 Vlad Pribiag<br />
Spin-orbit-mediated control of electron<br />
and hole spins in InSb nanowire quantum dots<br />
14:45 Reinhold Egger<br />
Majorana single-charge transistor<br />
15:30 Poster session<br />
17:00 Silvano De Franceschi<br />
Tunnel spectroscopy of hybrid quantum dots<br />
17:45 Seigo Tarucha<br />
Generation and detection of quantum coherence<br />
and entanglement with quantum dots<br />
18:30<br />
19:30 Conference dinner<br />
29
Talks Tuesday February 5<br />
Mercury Telluride, A Topological Insulator<br />
Hartmut Buhmann, University Würzburg, Germany<br />
The increasing un<strong>der</strong>standing of topological phases in condensed matter<br />
physics, which was initiated by the quantum Hall effect, has inspired the<br />
search for further topological states, especially, in the absence of magnetic<br />
fields. As an example a new topological insulator state, the quantum spin<br />
Hall (QSH) effect, was proposed for two-dimensional electron system with<br />
strong spin-orbit coupling [1,2] This new state is characterized by an insulating<br />
bulk and two counter-propagating helical edge states, which give rise<br />
for quantized conductance and propagating spin currents without dissipation.<br />
After the successful experimental demonstration of the QSH effect [3],<br />
the concept of topological insulators was extended to three-dimensional systems<br />
[4] where two-dimensional Dirac-like surface states dominate electronic<br />
and optical excitations resulting in new exotic properties.<br />
In this presentation, the material system of mercury-telluride (HgTe) is<br />
introduced. The realization of transport experiments in a two-dimensional<br />
topological insulator (TI) state is shown [5,6,7] which demonstrates the<br />
potential of the QSH effect for spin injection and detection in spintronics<br />
applications. Recently, the three-dimensional TI state has been realized in<br />
strained HgTe bulk layers [8]. The magneto-transport data show characteristic<br />
Hall-sequences of two independent 2D Dirac surfaces.<br />
1) C.L. Kane and E.J. Mele, Phys. Rev. Lett 95, 226801 (2005).<br />
2) B.A. Bernevig and S.C. Zhang, Phys. Rev. Lett. 96, 106802 (2006).<br />
3) M. König et al., Science 318, 766 (2007).<br />
4) L. Fu and C.L. Kane, Phys. Rev. B 76, 045302 (2007).<br />
5) M. König et al. Journ. Phys. Soc. Japn. 77, 031007 (2008).<br />
6) A. Roth et al., Science 325, 294 (2009).<br />
7) C. Brüne et al., Nature Physics 8, 485 (2012).<br />
8) C. Brüne et al., Phys. Rev. Lett. 106, 126803 (2011).<br />
30
Talks Tuesday February 5<br />
Notes<br />
31
Talks Tuesday February 5<br />
Electrical control of the Kondo effect in a helical edge liquid<br />
Henrik Johannesson, University of Gothenburg, Sweden<br />
Magnetic impurities affect the transport properties of the helical edge states<br />
of quantum spin Hall insulators by causing single-electron backscattering.<br />
We study such a system in the presence of a Rashba spin-orbit interaction<br />
induced by an external electric field, showing that this can be used to control<br />
the Kondo temperature, as well as the correction to the conductance due to<br />
the impurity. Surprisingly, for a strongly anisotropic electron-impurity spin<br />
exchange, Kondo screening may get obstructed by the presence of a noncollinear<br />
spin interaction mediated by the Rashba coupling. This challenges<br />
the expectation that the Kondo effect is stable against time-reversal invariant<br />
perturbations.<br />
32
Talks Tuesday February 5<br />
Notes<br />
33
Talks Tuesday February 5<br />
Resonantly Tunable Majorana Polariton in a Microwave Cavity<br />
Mircea Trif, UCLA, USA<br />
We study the spectrum of a one-dimensional Kitaev chain placed in a<br />
microwave cavity. In the o-resonant regime, the frequency shift of the cavity<br />
can be used to identify the topological phase transition of the coupled system.<br />
In the resonant regime, the topology of the system is sensitive to the presence<br />
of photons in the microwave cavity and, moreover, for a large number<br />
of photons (classical limit), the physics becomes similar to that of periodically-driven<br />
systems (Floquet insulators). We also analyze numerically a<br />
finite chain and show the existence of a degenerate subspace in the presence<br />
of the cavity that can be interpreted as a Majorana polariton.<br />
34
Talks Tuesday February 5<br />
Notes<br />
35
Talks Tuesday February 5<br />
Subgap states in Majorana wires<br />
Piet Brouwer, Freie Universität Berlin, Germany<br />
A one-dimensional spin-orbit coupled nanowire with proximity-induced<br />
pairing from a nearby s-wave superconductor may be in a topological nontrivial<br />
state, in which it has a zero energy Majorana bound state at each end.<br />
In this talk, I will discuss how non-idealities in this proposal, such as disor<strong>der</strong><br />
or deviations from a strict one-dimensional limit, affect the topological phase.<br />
36
Talks Tuesday February 5<br />
Notes<br />
37
Talks Tuesday February 5<br />
Spin-orbit-mediated control of electron and hole spins in InSb nanowire<br />
quantum dots<br />
Vlad Pribiag, Kavli Institute of Nanoscience Delft, The Netherlands<br />
The spin-orbit interaction allows fast control of individual spins in quantum dots<br />
using electric fields. Narrow-gap III-V semiconductor nanowires (InAs and InSb)<br />
exhibit strong spin-orbit coupling, which makes them a promising platform for spinbased<br />
qubits [1,2]. In this talk I will focus on InSb nanowires, which are of high<br />
interest both for qubits and for observing Majorana fermions.<br />
Using electric-dipole spin resonance (EDSR) we demonstrate coherent and universal<br />
control over the spin-orbit eigenstates of individual electrons, with Rabi<br />
frequencies in excess of 100 MHz and estimated fidelities of ∼ 81%. The large<br />
Zeeman energy difference between adjacent dots enables selective addressing of each<br />
qubit. Furthermore, we use EDSR in the strong interdot coupling regime to probe<br />
the strength and anisotropy of the spin-orbit coupling. The data in agreement with<br />
Rashba spin-orbit coupling, with α∼ 0.23 eVÅ. Although the Rabi oscillations for<br />
InSb nanowire qubits are consi<strong>der</strong>ably faster than for GaAs qubits, the coherence<br />
times are relatively short (Techo ∼ 35 ns) and show no significant dependence on<br />
driving frequency within the accessible range of 8-32 GHz. This is consistent with<br />
dephasing due to a fast spin bath that likely originates from the large nuclear spins<br />
of InSb (5/2 and 7/2 for 121Sb and 123Sb respectively, and 9/2 for In).<br />
A promising approach to enhancing qubit coherence is to use hole spins as qubits<br />
instead of electron spins because hole spins exhibit weaker hyperfine coupling [3].<br />
Taking advantage of the small bandgap of InSb, we can readily gate-tune our<br />
nanowire devices between few-electron and few-hole quantum dots [4]. Comparison<br />
between the two regimes suggests that the holes are primarily of light character and<br />
that the hyperfine interaction is about an or<strong>der</strong> of magnitude weaker for holes than<br />
for electrons. We demonstrate rotation of hole spin states via EDSR and use this<br />
to extract the hole g-factor, which is about an or<strong>der</strong> of magnitude smaller than for<br />
electrons. We compare the anisotropies of the g-factor and spin blockade leakage<br />
current for holes and electrons. The ability to control and read out hole spin states<br />
paves the way for coherent, all-electrical hole-spin qubits.<br />
[1] C. Flindt, A. S. Sørensen, K. Flensberg, Phys. Rev. Lett. 97 240501 (2006).<br />
[2] S. Nadj-Perge, S. M. Frolov, E. P. A. M. Bakkers, and L. P. Kouwenhoven,<br />
Nature 468, 1084 (2010).<br />
[3] D. Brunner, B. D. Gerardot, P. A. Dalgarno, G. Wüst, K. Karrai, N. G. Stoltz,<br />
P. M. Petroff, R. J. Warburton, Science 325, 70 (2009).<br />
[4] V. S. Pribiag, S. Nadj-Perge, S. M. Frolov, J. van den Berg, I. van Weperen,<br />
S. R. Plissard, E. P. A. M. Bakkers, and L. P. Kouwenhoven, Submitted.<br />
38
Talks Tuesday February 5<br />
Notes<br />
39
Talks Tuesday February 5<br />
Majorana single-charge transistor<br />
Reinhold Egger, Heinrich-Heine-Universität Düsseldorf, Germany<br />
I discuss quantum transport properties through a topological insulator<br />
nanowire with proximity-induced pairing correlations, where Majorana<br />
fermions are present at the ends as a consequence of strong spin-orbit interactions.<br />
When contacted by normal leads, and taking into account the charging<br />
energy, this Majorana single-charge transistor allows to study Majorana<br />
physics in a well-defined and relatively simple interacting model.<br />
40
Talks Tuesday February 5<br />
Notes<br />
41
Talks Tuesday February 5<br />
Tunnel spectroscopy of hybrid quantum dots<br />
Silvano De Franceschi, CEA, Grenoble, France<br />
Creating direct electrical connections between metal electrodes and lowdimensional<br />
semiconductor nanostructures has recently become possible<br />
thanks to the development of new nanomaterials and nanofabrication<br />
methods. Hybrid devices can thus be made in which macroscopic properties,<br />
such as superconductivity or ferromagnetism, are combined with microscopic<br />
properties, such as the charge or the spin state of individual electrons. Such<br />
hybrid devices open a wide range of opportunities for the study of new<br />
quantum phenomena and, in the long term, they may lead to the development<br />
of useful electronic devices with quantum functionalities.<br />
In this talk I will focus on hybrid devices made of zero-dimensional, quantumdot<br />
structures coupled to either normal or superconducting electrodes. I will<br />
present recent results obtained with hybrid devices made from self-assembled<br />
SiGe nanocrystals and InAs-based nanowires. Special attention will be<br />
devoted to the magnetic properties of the confined states in both normal and<br />
superconducting regime.<br />
42
Talks Tuesday February 5<br />
Notes<br />
43
Talks Tuesday February 5<br />
Generation and Detection of Quantum Coherence and Entanglement with<br />
Quantum Dots<br />
Seigo Tarucha, University of Tokyo, Japan<br />
Generation and detection of quantum coherence and entanglement is the core<br />
of quantum information processing. In this talk I will discuss new approaches<br />
to manipulate these concepts for electrons in semiconductor nanostructures.<br />
We have recently developed a two-path interferometer consisting of an<br />
Aharonov-Bohm ring connected to two tunnel-coupled quantum wires [1].<br />
Conventional AB rings are connected to two terminals and therefore suffer<br />
from phase rigidity which fixes the phase of AB oscillations at either 0 or<br />
π at zero-magnetic field. On the other hand, our interferometer operating<br />
in the non-adiabatic transport through the tunnel coupled wire does not<br />
suffer from the phase rigidity. We electrically control the dynamical phase<br />
through the AB ring and apply this technique to achieve full electrical control<br />
of a flying charge qubit defined by the presence of electron in either<br />
part of the two paths. We also use a similar interferometer but having a<br />
quantum dot in one of the two AB ring arms to detect the transport phase<br />
through the dot. We observe a well-defined π/2 phase through the dot when<br />
the dot is in the Kondo regime.<br />
The concept of non-local entanglement is well established for correlated<br />
photon pairs, but not yet for electrons in solid state systems. We have<br />
studied non-local entanglement using double dot Josephson junctions. The<br />
splitting of Cooper pairs into both dots may contribute to generate supercurrent,<br />
because Cooper pair tunneling through the same dot is strongly<br />
suppressed by the electron-electron interaction [2]. We observe the supercurrent<br />
depending on the double dot charge state and discuss the contribution<br />
from the split Cooper pair tunneling to the supercurrent.<br />
[1] M. Yamamoto et al. Nature Nanotechnology, 7, 247 (2012).<br />
[2] Y. Kanai et al. Appl. Phys. Lett. 100, 202109 (2012).<br />
44
Talks Tuesday February 5<br />
Notes<br />
45
Talks Tuesday February 5<br />
46
Talks Wednesday February 6<br />
Talks Wednesday February 6<br />
Wednesday (Feb. 6)<br />
9:00 Christian Schönenberger<br />
Interference and interaction in ultraclean<br />
suspended monolayer and bilayer graphene<br />
9:45 Bernd Braunecker<br />
Spin-orbit interaction in carbon nanotubes<br />
and its utility for proving entanglement of electrons<br />
10:30 Coffee break<br />
11:00 Kasper Grove-Rasmussen<br />
Level structure and tunnel coupling of carbon nanotube quantum dots<br />
11:45 Charlie Marcus<br />
(to be announced)<br />
12:30 Lunch<br />
Talks of the Research Unit<br />
Coherence and Relaxation Properties of Electron Spins<br />
All participants of the workshop are invited.<br />
14:00 Y. Mokrousov<br />
Engineering Chern insulators with spin and orbital degrees of freedom<br />
14:25 R. Steinigeweg<br />
Real-time dynamics of spin-currents in quantum magnets:<br />
Coherence and momentum dependence<br />
14:50 V. Kataev<br />
ESR spectroscopy on spin-orbital Mott insulators<br />
15:15 S. Müller<br />
Magnetic field effects on the finite-frequency noise<br />
and ac conductance of a Kondo quantum dot out of equilibrium<br />
15:40 B. Büchner<br />
Quasi-ballistic transport of Dirac fermions in Bi2Se3 nanowires<br />
16:05 Coffee break<br />
16:30 I. Stepanov<br />
Spintronics without ferromagnets<br />
16:55 C. Honerkamp<br />
Interacting ground states of few-layer graphene<br />
17:10 B. Beschoten<br />
Spin transport in graphene<br />
17:35 C. Volk<br />
Probing relaxation times in graphene quantum dots<br />
18:05 P. Struck<br />
Nanomechanical read-out of a single spin<br />
18:20 End of the workshop<br />
47
Talks Wednesday February 6<br />
Interference and interaction in ultraclean suspended monolayer and bilayer<br />
graphene<br />
Christian Schönenberger, University of Basel, Switzerland<br />
We first show that graphene (monolayer and bilayer) with exceptional high<br />
mobilities approaching 100 m 2 /Vs can be obtained when suspended and insitu<br />
current annealed. Using such materials, we then first summarize recent<br />
results obtained with bilayer graphene where a pronounced gap emerges at<br />
the charge-neutrality point. This gap forms in zero electric and magnetic field<br />
and is thought to be accompanied by a transition into a broken symmetry<br />
state. The precise nature of this ground state is currently debated. We show<br />
that our results are consistent with both the layer anti-ferromagnetic state<br />
(LAF) and the quantum-spin Hall state (QSH). While we cannot distinguish<br />
these two states, we can exclude the quantum anomalous Halls state based<br />
on electrical measurements in parallel magnetic field.<br />
We further will demonstrate electrical transport experiments in monolayer<br />
graphene with top gates arranged in the form of strips. The gates allow to<br />
define n-p regions yielding a peculiar interference pattern in high mobility<br />
samples caused by Klein tunneling.<br />
Coauthors:<br />
Frank Freitag, Peter Rickhaus, Romain Maurand, Jelena Trbovic, Markus<br />
Weiss and Christian Schönenberger<br />
48
Talks Wednesday February 6<br />
Notes<br />
49
Talks Wednesday February 6<br />
Spin-orbit interaction in carbon nanotubes and its utility for proving entanglement<br />
of electrons<br />
Bernd Braunecker, Universidad Autónoma de Madrid, Spain<br />
I will discuss spin-orbit interaction in carbon nanotubes and show that it<br />
has distinct features that allow to obtain information on the entanglement of<br />
injected pairs of electrons. I will briefly review the form of spin-orbit interaction<br />
in single-wall nanotubes, and demonstrate that it leads to a perfect<br />
spin filter with spin orientations that are tunable by external fields. Based on<br />
this, I will focus on a Cooper pair splitter setup and show that the tunable<br />
spin-filtering allows to implement entanglement detectors, such as probing a<br />
Bell inequality. These detectors can rely on conductance measurements alone<br />
and do not require the precise knowledge of the spin orientations of the spin<br />
filter. Yet if in addition the spin orientations are known, the same setup can<br />
be used for full quantum state tomography.<br />
50
Talks Wednesday February 6<br />
Notes<br />
51
Talks Wednesday February 6<br />
Level structure and tunnel coupling of carbon nanotube quantum dots<br />
Kasper Grove-Rasmussen, University of Copenhagen, Denmark<br />
We present our current un<strong>der</strong>standing of the quantum states in a carbon<br />
nanotube quantum dot deduced from low temperature transport measurements<br />
in parallel and perpendicular magnetic fields. The observed energy<br />
spectrum is shown to be or<strong>der</strong>ed in shells of two doublets consistent with a<br />
single-particle four-state model including spin-orbit interaction, intra-shell<br />
valley mixing and an orbital g-factor. To fully capture the behavior in the<br />
multi-shell case, additional inter-shell valley mixing parameters are needed,<br />
describing valley mixing between states belonging to different shells [1, 2].<br />
Furthermore, for certain shells, the two doublets are observed to be differently<br />
coupled to the leads, resulting in gate-dependent level renormalization.<br />
By comparison to the one-shell model this is shown to be a consequence<br />
of intra-shell valley mixing in the nanotube. Moreover, a parallel magnetic<br />
field is shown to reduce this mixing and thus suppress the effects of tunnelrenormalization<br />
[3].<br />
[1] T. Sand Jespersen, K. Grove-Rasmussen, J. Paaske, K. Muraki, T. Fujisawa,<br />
J. Nygård, and K. Flensberg, Nat. Phys. 7, 348 (2011).<br />
[2] T. S. Jespersen, K. Grove-Rasmussen, K. Flensberg, J. Paaske, K.<br />
Muraki, T. Fujisawa, and J. Nygård, Phys. Rev. Lett. 107, 186802 (2011)<br />
[3] K. Grove-Rasmussen, S. Grap, J. Paaske, K. Flensberg, S. An<strong>der</strong>gassen,<br />
V. Meden, H. I. Jørgensen, K. Muraki, and T. Fujisawa, Phys. Rev. Lett.<br />
108, 176802 (2012).<br />
52
Talks Wednesday February 6<br />
Notes<br />
53
Talks Wednesday February 6<br />
(to be announced)<br />
Charles Marcus, University of Copenhagen, Denmark<br />
(to be announced)<br />
54
Talks Wednesday February 6<br />
Notes<br />
55
Posters Monday February 4<br />
Poster program & abstracts<br />
Posters Monday February 4<br />
Time: 15:30 - 17:00<br />
Poster numbers: 1-20<br />
Topics:<br />
Atomic and molecular scale devices<br />
Semiconductor quantum dots and wires<br />
57
Posters Monday February 4<br />
Poster 1:<br />
Dynamical spin and charge excitations with spin–orbit coupling in 3d adatoms<br />
on Cu(111) and Pt(111)<br />
Manuel dos Santos Dias<br />
The presence of spin–orbit coupling has a fundamental impact on the<br />
magnetic excitation spectrum: there is a finite gap at zero frequency and<br />
spin and charge excitations become coupled. The excitation spectrum is<br />
<strong>der</strong>ived from the dynamical magnetic susceptibility of the electronic system,<br />
for which we developed a formalism based on Time–Dependent Density<br />
Functional Theory, as implemented in the Korringa–Kohn–Rostoker Green<br />
function method [1,2]. As an application, we present first–principles calculations<br />
of the charge, longitudinal and transverse magnetic excitations of<br />
3d adatoms deposited on the Cu(111) and Pt(111) surfaces. Focus is on<br />
the expected spin–charge coupling induced by the the spin–orbit interaction,<br />
and on the dynamical anisotropic effects that generalize the familiar<br />
magnetic anisotropy.<br />
Work supported by the HGF-YIG Programme FunSiLab – Functional<br />
Nanoscale Structure Probe and Simulation Laboratory (VH-NG-717).<br />
[1] S. Lounis, A. T. Costa, R. B. Muniz and D. L. Mills, Phys. Rev. Lett.<br />
105, 187205 (2010)<br />
[2] S. Lounis, A. T. Costa, R. B. Muniz and D. L. Mills, Phys. Rev. B 83,<br />
035109 (2011)<br />
58
Posters Monday February 4<br />
Poster 2:<br />
Spintronic molecular magnetism: zero field splitting without spin-orbit coupling<br />
Michael Hell<br />
Single-molecule magnets (SMMs) and magnetic adatoms have been studied<br />
intensely mainly because of their large spin anisotropy. In these systems,<br />
a spin-anisotropy barrier arises from internal quantum fluctuations due to<br />
strong spin-orbit interaction. However, such a spin-anisotropy barrier can<br />
also be externally induced into an intrinsically spin-isotropic system by coupling<br />
it to an spin-anisotropic environment.<br />
We illustrate this new idea for an interacting quantum dot (QD) with a high<br />
spin S>1/2, tunnel-coupled to spin-polarized electrodes. Besides dissipative<br />
effects, multi-spin currents generate an additional coherent time evolution<br />
of the QD, which is described by an effective Hamiltonian. The latter contains<br />
the dipolar exchange field [1-3], well known from spintronics, and an<br />
additional, new exchange field coupling to the spin-quadrupole moment of<br />
the QD. This spintronic spin-anisotropy barrier can be comparable in size to<br />
that of SMMs, but grants the additional flexibility of electric and magnetic<br />
tunability.<br />
We compare these analytic results, obtained by a perturbative treatment<br />
of the tunnel-couplings, to predictions by DM-NRG calculations accessing<br />
the strong coupling regime. We show that transport characteristics can be<br />
used to directly read out the quadrupolar field, utilizing its competition<br />
with Kondo spin-exchange processes with the ferromagnets. Furthermore,<br />
the quadrupolar exchange field can dominate over the dipolar exchange field,<br />
thereby strongly enhancing the low-temperature spin-filtering as compared<br />
to spin-1/2 QD spin-valves.<br />
References:<br />
[1] J. Martinek et al., Phys. Rev. Lett. 91, 127203 (2003); Phys. Rev. B 72,<br />
121302 (2005).<br />
[2] J. Hauptmann et al., Nature Phys. 4, 373 (2008).<br />
[3] M. Gaass et al., Phys. Rev Lett. 107, 176808 (2011).<br />
[4] M. Baumgärtel et al., Phys. Rev. Lett. 107, 087202 (2011)<br />
Coauthors<br />
M. Misiorny and M. R. Wegewijs<br />
59
Posters Monday February 4<br />
Poster 3:<br />
Influence of magnetic anisotropy on the un<strong>der</strong>screened Kondo effect in the<br />
presence of ferromagnetism<br />
Maciej Misiorny<br />
The prominent role of magnetic anisotropy (MA) in formation of the Kondo<br />
effect has recently been demonstrated experimentally [1,2]. In particular, it<br />
turned out that in systems of spin S>1/2, such as magnetic adatoms (i.e.<br />
Fe, Co or Mn) or magnetic molecules, the Kondo effect can be tuned by<br />
modifying the system’s MA. Furthermore, theoretical studies also indicate<br />
that MA can be a key factor determining spin-polarized transport through<br />
a magnetic nanosystem [3]. Motivated by the recent experiment [2], in this<br />
communication we address how the MA affects the un<strong>der</strong>screened Kondo<br />
effect (i.e. partial compensation of the molecular spin by conduction electrons)<br />
in the case of an artificial molecule of spin S=1 coupled to a reservoir<br />
of spin-polarized conduction electrons [4]. The crucial ingredient of the model<br />
is the presence of uniaxial MA. The problem is analyzed by means of Wilson’s<br />
numerical renormalization group (NRG) method, which allows for calculating<br />
the spectral function of the molecule. We show that the interplay of MA and<br />
ferromagnetism has a fundamental significance for occurring of the Kondo<br />
effect. Most importantly, despite the presence of the effective exchange field<br />
[5] the Kondo effect can be restored by adjusting the magnitude of MA.<br />
1. A.F. Otte et al., Nature Phys. 4, 847 (2008).<br />
2. J.J. Parks et al., Science 328, 1370 (2010).<br />
3. M. Misiorny, I. Weymann and J. Barnas, Phys. Rev. Lett. 106, 126602<br />
(2011); Phys. Rev. B 84, 035445 (2011).<br />
4. I. Weymann and L. Borda, Phys. Rev. B 81, 115445 (2010).<br />
5. J. Martinek et al., Phys. Rev. Lett. 91, 127203 (2003); Phys. Rev. B 72,<br />
121302 (2005).<br />
Coauthors<br />
I. Weymann and J. Barnaś<br />
60
Posters Monday February 4<br />
Poster 4:<br />
Kondo effect and magnetic frustration in a system of magnetic trimer on a<br />
metal surface<br />
Hoa Nghiem<br />
We use quantum Monte Carlo simulation to clarify the competition between<br />
Kondo screening and magnetic frustration in a system of three magnetic<br />
adatoms on a metal surface [1]. We observe the feature of spectral density<br />
depending on the geometric configuration of three magnetic adatoms on the<br />
surface [2, 3]. In the isosceles configuration, the spectral density exhibits a<br />
significant peak near the Fermi level, which we attribute to the Yosida-Kondo<br />
resonance. In the equilateral configuration, no peak is observed near the<br />
Fermi level. This observation suggests the two separate regimes; the Yosida-<br />
Kondo dominant regime with the singlet ground state, and the magnetic<br />
frustration dominant regime with the degenerate ground state, - changing<br />
from one regime to another is realized as we gradually switch the geometric<br />
configuration from the isosceles triangle to equilateral one. By calculating<br />
the spectral density and the magnetic susceptibility in a wide range of temperatures,<br />
we prove the existence of the two separate regimes and suggest<br />
the critical crossover between them.<br />
[1] N. T. M. Hoa, W. A. Dino, and H. Kasai: J. Phys. Soc. Jpn. 81 (2012)<br />
023706.<br />
[2] T. Jamneala, V. Madhavan, and M. F. Crommie: Phys. Rev. Lett 87<br />
(2001) 256804.<br />
[3] N. T. M. Hoa, W. A. Dino, and H. Kasai: J. Phys. Soc. Jpn. 79 (2010)<br />
113706.<br />
Poster 5:<br />
Spin dynamics in nanoparticles near Stoner instability<br />
Philipp Stegmann<br />
We analyse the spin dynamics of a nanoparticle close to the Stoner instability.<br />
The nanoparticle is weakly tunnel coupled to two ferromagnetic leads. By<br />
mapping to an effective Fokker-Planck description we identify two different<br />
types of dynamic behaviour (diffusion vs. drift), which are revealed by characteristic<br />
relaxation times and a Fano factor that oscillates as a function of an<br />
applied bias voltage. Finally, we propose biasing schemes to generate states<br />
with magnetic quadrupole moments that dominate over a negligible dipole<br />
moment.<br />
61
Posters Monday February 4<br />
Poster 6:<br />
Nonequilibrium transport through quantum dots with Dzyaloshinskii-Moriya<br />
interactions<br />
Mikhail Pletyukhov<br />
We study nonequilibrium transport through a single-orbital An<strong>der</strong>son<br />
model in a magnetic field with spin-dependent hopping amplitudes. In<br />
the cotunneling regime it is described by an effective spin-1/2 dot with a<br />
Dzyaloshinsky-Moriya-Kondo (DMK) interaction between the spin on the<br />
dot and the electron spins in the leads. Using a real-time renormalization<br />
group technique we show that at low temperatures (i) the DMK interaction<br />
is strongly renormalized, (ii) the renormalized magnetic field acquires a linear<br />
voltage dependence, and (iii) the differential conductance exhibits a voltage<br />
asymmetry which is strongly enhanced by logarithmic corrections. We propose<br />
transport measurements in which these signatures can be observed.<br />
62
Posters Monday February 4<br />
Poster 7:<br />
Spin-Orbit interactions and the Kondo effect<br />
Nancy Sandler<br />
Recent studies [1] have pointed out that the thermodynamics of the Kondo<br />
effect are essentially unaltered by the presence of Rashba spin-orbit interactions<br />
in a host two-dimensional electron gas. However, it has also been<br />
proposed [2]that the presence of bulk Rashba interactions induces a coupling<br />
between a magnetic impurity and conduction electrons with nonzero orbital<br />
angular momentum about the impurity site. This coupling appears as a<br />
combination of the standard Kondo exchange and the Dzyaloshinskii-Moriya<br />
interaction that, in the appropriate regime, produces an exponential enhancement<br />
of the Kondo temperature. In this work we review previous works and<br />
present recent results obtained by using the numerical renormalization group.<br />
In agreement with previous studies, we find only minor changes in the Kondo<br />
temperature scale when the Rashba coupling is increased at fixed Fermi<br />
energy. However, for fixed band filling, increasing the spin-orbit coupling can<br />
move the Fermi energy near to a Van Hove singularity in the effective density<br />
of states, leading to an exponential enhancement of the Kondo scale. Static<br />
spin correlations confirm that the impurity couples to conduction channels<br />
of nonzero orbital angular momentum. We also explore the effects of a magnetic<br />
field applied in the plane of the host system and extend our results to<br />
graphene systems.<br />
[1] J. Malecki, J. Stat. Phys. 129, 741 (2007); R. Zitko and J. Bonca, Phys.<br />
Rev. B 84, 193411 (2011).<br />
[2] M. Zarea, S. Ulloa and N. Sandler, Phys. Rev. Lett. 108, 046601 (2012).<br />
63
Posters Monday February 4<br />
Poster 8:<br />
Influence of Noise on the Exchange-Only Qubit<br />
Sebastian Mehl<br />
Spin qubits have attracted interest as one realization scheme to achieve<br />
quantum computation in a solid state system. Encoding qubits into more<br />
than one quantum dot has turned out to be experimentally very favorable.<br />
When encoding a qubit into three quantum dots one can show that electrostatic<br />
bias offers full control of the qubit. It generates tunable exchange<br />
interactions between neighboring quantum dots. We present the influence<br />
of noise on the exchange-only qubit and discuss coherence properties. We<br />
especially point out how the definition of the qubit in the embedding Hilbert<br />
space can lead to different coherence properties.<br />
Poster 9:<br />
Effect of many-body correlations on mesoscopic charge relaxation<br />
Jonckheere Thibaut<br />
We investigate nonperturbatively the charge relaxation resistance and<br />
quantum capacitance in a coherent RC circuit in the strong-coupling regime.<br />
We find that the many-body correlations break the universality in the charge<br />
relaxation resistance: (i) The charge relaxation resistance has peaks at finite<br />
frequencies Γ/ , where Γ is an effective level broadening, and (ii) the zerofrequency<br />
resistance deviates from the universal value when the Zeeman splitting<br />
is comparable to Γ. This behavior becomes even more prominent in<br />
the Kondo regime. The observed features are ascribed to the generation<br />
of particle-hole excitations in the contacts accomplished by spin-flip processes<br />
in the dot.<br />
64
Posters Monday February 4<br />
Poster 10:<br />
Interplay of Coulomb interaction and spin-orbit effects in multi-level quantum<br />
dots<br />
Stephan Grap<br />
We study electron transport through a multi-level quantum dot with Rashba<br />
spin-orbit interaction in the presence of local Coulomb repulsion. Motivated<br />
by recent experiments, we compute the level splitting induced by the spinorbit<br />
interaction at finite Zeeman fields B, which provides a measure of<br />
the renormalized spin-orbit energy. This level splitting is responsible for<br />
the suppression of the Kondo ridges at finite B characteristic for the multilevel<br />
structure. In addition, the dependence of renormalized g-factors on<br />
the relative orientation of the applied B field and the spin-orbit direction<br />
following two different protocols used in experiments is investigated.<br />
Poster 11:<br />
Transport properties of a multichannel Kondo dot in a magnetic field<br />
Christoph Hörig<br />
We study the nonequilibrium transport through a multichannel Kondo<br />
quantum dot in the presence of a magnetic field. We use the exact solution<br />
of the two-loop renormalization group equation to <strong>der</strong>ive analytical results<br />
for the g-factor, the spin relaxation rates, the magnetization, and the differential<br />
conductance. We show that the finite magnetization leads to a coupling<br />
between the conduction channels which manifests itself in additional features<br />
in the differential conductance.<br />
65
Posters Monday February 4<br />
Poster 12:<br />
An alternative functional renormalization group approach to the single impurity<br />
An<strong>der</strong>son model<br />
Michael Kinza<br />
We present an alternative functional renormalization group (fRG) approach<br />
to the single-impurity An<strong>der</strong>son model at finite temperatures. Starting<br />
with the exact self-energy and interaction vertex of a small system (’core’)<br />
containing a correlated site, we switch on the hybridization with a noninteracting<br />
bath in the fRG-flow and calculate spectra of the correlated site.<br />
Different truncations of the RG-flow-equations and choices of the core are<br />
compared and discussed. Furthermore we calculate the linear conductance<br />
and the magnetic susceptibility as functions of temperature and interaction<br />
strength. The signatures of Kondo physics arising in the flow are compared<br />
with numerical renormalization group results.<br />
Poster 13:<br />
Conductance scaling in Kondo correlated quantum dots: role of level asymmetry<br />
Lukas Merker<br />
The low temperature electrical conductance through correlated quantum dots<br />
provides a sensitive probe of the physics (e.g., of Fermi-liquid vs non-Fermiliquid<br />
behavior) of such systems. Here, we investigate the role of level asymmetry<br />
(gate voltage) and local Coulomb repulsion (charging energy) on the<br />
low temperature and low field scaling properties of the linear conductance of a<br />
quantum dot described by the single level An<strong>der</strong>son impurity model. We use<br />
the numerical renormalization group and renormalized perturbation theory<br />
to quantify the regime of gate voltages and charging energies where universal<br />
Kondo scaling may be observed and also quantify the deviations from this<br />
universal behavior with increasing gate voltage away from the Kondo regime<br />
and with decreasing charging energy. Our results could be a useful guide for<br />
detailed experiments on conductance scaling in semiconductor and molecular<br />
quantum dots exhibiting the Kondo effect.<br />
Coauthors<br />
T. A. Costi, E. Munoz, S. Kirchner<br />
66
Posters Monday February 4<br />
Poster 14:<br />
Fermionic superoperators in application to non-linear transport: real-time<br />
renormalization group, time-evolution and exact relations for An<strong>der</strong>son<br />
quantum dots.<br />
Roman Saptsov<br />
We introduced a new formalism of fermionic superoperators in Liouville-<br />
Fock space to enable a real-time renormalization group analysis of the nonequilibrium<br />
An<strong>der</strong>son model in the stationary state. The RT-RG equations<br />
were solved numerically including both 1- and 2- loop or<strong>der</strong>s in the limit of<br />
zero temperature and non-linear transport voltages where most standard theoretical<br />
methods break down. We predict non-perturbative tunneling effects<br />
in the transport stability diagram which can be measured experimentally.<br />
Moreover, we found the exact functional form of the renormalized spectra of<br />
the dot at any loop or<strong>der</strong>. In the strong-interacting limit the method breaks<br />
down as expected only at very small voltages on the or<strong>der</strong> of the Kondo<br />
temperature, which we illustrate by comparison with the Friedel sum rule.<br />
For the time dependent non-interacting case with help of fermionic superoperators<br />
we show that the perturbation expansion in tunnel coupling automatically<br />
truncates at the second loop and discuss solutions in the Wide Band<br />
Limit and beyond of it. We also discuss extension of our time-dependent<br />
results to the weakly interacting case.<br />
67
Posters Monday February 4<br />
Poster 15:<br />
Mechanism for Giant Thermopower in Negative-U Molecular Quantum Dots<br />
Theo Costi<br />
We investigate with the aid of numerical renormalization group techniques<br />
the thermoelectric properties of a molecular quantum dot described by the<br />
negative-U An<strong>der</strong>son model. We show that the charge Kondo effect provides<br />
a mechanism for enhanced thermoelectric power via a correlation-induced<br />
asymmetry in the spectral function close to the Fermi level. We show that<br />
this effect results in a dramatic enhancement of the Kondo-induced peak in<br />
the thermopower of negative-U systems with Seebeck coefficients exceeding<br />
50 µV/K over a wide range of gate voltages [1,2].<br />
[1] S. An<strong>der</strong>gassen, T. A. Costi and V. Zlatic, Phys. Rev. B 84, 241107 (R)<br />
(2011)<br />
[2] T. A. Costi and V. Zlatic, Phys. Rev. Lett. {bf 108}, 36402 (2012); in<br />
"New Materials for Thermoelectric Applications: Theory and Experiment",<br />
ed. V. Zlatic and A. C. Hewson, ISBN 978-94-007-4983-2 (Springer, Berlin,<br />
2012)<br />
Coauthors: S. An<strong>der</strong>gassen and V. Zlatic<br />
Poster 16:<br />
Boltzmann-type approach to thermal drag in spin-1/2-lad<strong>der</strong> systems coupled<br />
to phonons<br />
Christian Bartsch<br />
We quantitatively investigate the spin-phonon drag contributions to the<br />
thermal conductivity of a two-leg-spin-1/2-lad<strong>der</strong> coupled to lattice vibrations<br />
in a magnetoelastic way. By applying suitable transformations the<br />
system is mapped onto a weakly interacting quantum gas model of bosonic<br />
spin excitations (magnons) and phonons. We adequately construct a collision<br />
term of a linear(ized) Boltzmann equation from the un<strong>der</strong>lying quantum<br />
dynamics by means of a pertinent projection operator technique. From the<br />
Boltzmann equation we obtain concrete numerical values for the drag conductivity<br />
and relate it to the individual thermal conductivities of magnons and<br />
phonons for parameter ranges which are typical for certain material classes.<br />
68
Posters Monday February 4<br />
Poster 17:<br />
Rashba spin-orbit interaction in a quantum wire superlattice<br />
Sigurdur I. Erlingsson<br />
We study the effects of a longitudinal periodic potential on a parabolic<br />
quantum wire, and long quantum point contacts, defined in a two-dimensional<br />
electron gas with Rashba spin-orbit interaction. For an infinite wire<br />
superlattice we find that the energy gaps are shifted away from the usual<br />
Bragg planes due to the Rashba spin-orbit interaction. We have also calculated<br />
the charge conductance through a periodic potential of a finite length<br />
via the nonequilibrium Green’s function method combined with the Landauer<br />
formalism. We find dips in the conductance that correspond well to<br />
the energy gaps of the infinite wire superlattice. From the infinite wire energy<br />
dispersion, we <strong>der</strong>ive an equation relating the location of the conductance<br />
dips as a function of the Fermi energy to the Rashba spin-orbit coupling<br />
strength. We propose that the strength of the Rashba spin-orbit interaction<br />
can be extracted via a charge conductance measurement.<br />
Poster 18:<br />
Electronic states in a cylindrical nanowire in magnetic and electric fields<br />
Andrei Manolescu<br />
Single particle states of electrons situated on a closed cylindrical surface of<br />
radius 30-100 nm are calculated. The length of the cylin<strong>der</strong> may be either<br />
infinite or finite. In the presence of a magnetic field uniform in space, but perpendicular<br />
to the longitudinal axis of the cylin<strong>der</strong>, the orbital effects depend<br />
on the radial component of the magnetic field. For a sufficiently strong field,<br />
when the magnetic length becomes comparable to the radius of the cylin<strong>der</strong>,<br />
the orbital motion corresponds to closed cyclotron orbits in the regions with<br />
strong radial field, but to open quasi one-dimensional snaking orbits in the<br />
regions where the radial field vanishes and changes sign. The energy of the<br />
cyclotron states increases with the magnetic field relatively to the energy of<br />
the snaking states such that at high magnetic fields the electrons concentrate<br />
around the snaking orbits. The spin of the electron is included via Zeeman<br />
and Rashba spin-orbit effects. A uniform electric field perpendicular to the<br />
cylin<strong>der</strong> is also consi<strong>der</strong>ed, as being produced by a metallic electrode placed<br />
near the cylin<strong>der</strong>. In this case the spin-orbit coupling becomes anisotropic.<br />
Attempts to include Coulomb effects in the Hartree-Fock approximation are<br />
discussed.<br />
69
Posters Monday February 4<br />
Poster 19:<br />
Quantized conductance in InSb nanowires and electrical characterization of<br />
branched InSb nanowires<br />
Ilse van Weperen<br />
Indium antimonide (InSb) nanowires have shown potential for creation of<br />
topological superconducting and helical liquid states. We report on transport<br />
measurements of single high-mobility indium antimonide nanowires and<br />
branched InSb nanowires.<br />
A novel growth mechanism allows two InSb nanowires to merge into a nano-<br />
T or nanocross. Transport measurements of branched nanowires show characteristics<br />
similar to that of single nanowires. Magnetoresistance measurements<br />
of nanocrosses allow extraction of nanowire electron density.<br />
A mean free path of ∼ 300 nm in InSb nanowires enables observation of<br />
one-dimensional conductance channels at high (B > 2 T) magnetic fields.<br />
Conductance quantization is studied as a function of magnetic field and bias<br />
voltage, enabling extraction of an effective g-factor of ∼ 65 and a subband<br />
spacing of ∼ 15 meV.<br />
Poster 20:<br />
Phase-Coherent Transport and Spin-Orbit Coupling in InAs Nanowires<br />
Sebastian Heedt<br />
We report on phase-coherent transport measurements on differently doped<br />
InAs nanowires grown by selective area metalorganic vapor phase epitaxy.<br />
The nanowires are contacted individually and the low-temperature electronic<br />
transport properties are investigated for temperatures down to 30 mK and<br />
magnetic fields up to 10 T. To this end, top-gates with high-k dielectrics are<br />
prepared. At small current-bias the transport is phase-coherent and gives<br />
us the opportunity to determine the phase-coherence length and the spin<br />
relaxation length. The band profile and the carrier concentration of the<br />
nanowires can be manipulated by the application of a gate voltage. An analytical<br />
model for the low-field quantum conductivity correction is utilized<br />
to quantify Rashba and Dresselhaus spin-orbit coupling effects. Nanowires<br />
with different doping concentrations are investigated to gain information<br />
on how the doping of the highly spin-orbit coupled InAs nanowires impacts<br />
the spin-lifetime.<br />
70
Posters Tuesday February 5<br />
Posters Tuesday February 5<br />
Time: 15:30 - 17:00<br />
Poster numbers: 21-43<br />
Topics:<br />
Spin-orbit hybrid systems<br />
Carbon nanotubes and graphene<br />
71
Posters Tuesday February 5<br />
Poster 21:<br />
Optical Josephson radiation from a Majorana Josephson junction<br />
Christoph Ohm<br />
We consi<strong>der</strong> a voltage-biased Josephson junction between two nanowires<br />
hosting Majorana fermions which occur as topological protected zero-energy<br />
excitations at the junction. We show that two Majorana fermions localized<br />
at the junction, though being neutral excitations, interact with the electromagnetic<br />
field and generate coherent radiation similar to the conventional<br />
Josephson radiation in a voltage biased Josephson junction. Within a semiclassical<br />
analysis of the light field, we find that the optical phase gets locked<br />
to the superconducting phase difference and that the radiation is emitted<br />
at half of the Josephson frequency. In or<strong>der</strong> to confirm the coherence of<br />
the radiation, we study correlations of the light emitted by two spatiallyseparated<br />
junctions in a SQUID geometry taking into account decoherence<br />
by spontaneous phase-switchings due to quasi-particle poisoning as well as<br />
by thermal effects.<br />
Poster 22:<br />
Spin-flip excitations induced by time-dependent electric fields in surfaces with<br />
strong spin-orbit interaction<br />
Julen Ibanez<br />
Heavy element surfaces have become an ideal testing ground for investigating<br />
the nature and effects of the relativistic spin-orbit interaction in low<br />
dimensional systems. In this work, we study spin-flip transitions between the<br />
metallic surface states of the Pb/Ge(111) and the Rashba prototype Au(111)<br />
surfaces. We calculate the spin-flip matrix elements following an approach<br />
based on the interpolation of maximally localized Wannier functions. The<br />
obtained results show that spin-flip absorptions are one or<strong>der</strong> of magnitude<br />
larger in Pb/Ge(111) than in Au(111), reaching a remarkable maximum of<br />
6% absorption of the total irradiated light.<br />
We find that the enhanced spin-flip contribution in Pb/Ge(111) is closely<br />
connected to the behavior of the momentum dependent spin-polarization<br />
associated to the surface states.<br />
72
Posters Tuesday February 5<br />
Poster 23:<br />
Quantum Dots and Majorana Fermions<br />
Martin Leijnse<br />
Majorana fermions, particles which are their own anti-particles, may or may<br />
not exist as elementary particles in nature. However, it was shown theoretically<br />
a few years ago that they can appear as quasiparticle excitations in<br />
certain condensed matter systems combining superconductivity, magnetism,<br />
and strong spin-orbit coupling. This has quickly become one of the hottest<br />
topics in mesoscopic physics research, partly because of the possibility to use<br />
Majorana fermions for quantum information processing.<br />
I will present work suggesting a new and perhaps easier way to generate<br />
Majorana-like bound states in a double quantum dot system, where the dots<br />
are tunnel coupled to each other via a superconductor. I will also show that<br />
quantum dots can be used to do more accurate spectroscopy of Majorana<br />
systems, and even to manipulate quantum information stored in Majoranabased<br />
qubits.<br />
Poster 24:<br />
Disor<strong>der</strong>-induced topological phase transitions in a quasi-1D spinless p-wave<br />
superconductor<br />
Maria-Theresa Rie<strong>der</strong><br />
Topological phases and the surface states associated with them are known<br />
to be robust against weak disor<strong>der</strong> and to break down at a critical disor<strong>der</strong><br />
strength. In this letter we show how disor<strong>der</strong> induces a series of topological<br />
phase transitions in a spinless multichannel p-wave superconducting<br />
wire. We find that the wire alternates between topologically trivial and nontrivial<br />
phases as the induced superconductivity is increased in a perturbative<br />
approach to the transverse coupling.<br />
73
Posters Tuesday February 5<br />
Poster 25:<br />
Majorana modes and complex band structure of quantum wires<br />
Llorens Serra<br />
We describe Majorana edge states of a semi-infinite wire using the complex<br />
band structure approach. In this method the edge state at a given energy is<br />
built as a superposition of evanescent waves. It is shown that the superposition<br />
can not always satisfy the required boundary condition, thus restricting<br />
the existence of edge modes. We discuss purely 1D and 2D systems, focussing<br />
in the latter case on the effect of the Rashba mixing term. We also review<br />
recent results on the calculation of Majorana modes in finite systems and of<br />
the linear transport within a coupled-channels model.<br />
References:<br />
[1] Majorana modes and complex band structure of quantum wires, L. Serra,<br />
arXiv:1210.4817<br />
[2] Transport through Majorana nanowires attached to normal leads, J.S.<br />
Lim, R. Lopez and L. Serra, New J. Phys. 14, 083020 (2012).<br />
[3] Magnetic field instability of Majorana modes in multiband semiconductor<br />
wires, J.S. Lim, L. Serra, R. Lopez and R. Aguado, Phys. Rev. B 86,<br />
121103(R) (2012).<br />
74
Posters Tuesday February 5<br />
Poster 26:<br />
Interaction induced charge and spin pumping in non-linear transport through<br />
a quantum dot<br />
Hernan Calvo<br />
We investigate charge and spin transport through an adiabatically driven,<br />
strongly interacting quantum dot weakly coupled to two metallic contacts<br />
with finite bias voltage. Within a kinetic/master equation approach we identify<br />
coefficients of response to the time-dependent external driving and relate<br />
these to the concepts of charge and spin emissivities in the time-dependent<br />
scattering matrix approach. Expressed in terms of auxiliary vector fields the<br />
response coefficients allow for a straightforward analysis of recently predicted<br />
interaction-induced pumping un<strong>der</strong> periodic modulation of the gate and bias<br />
voltage [1]. We perform a detailed study of this effect and the related adiabatic<br />
Coulomb blockade spectroscopy, and, in particular, extend it to spin<br />
pumping. Analytic formulas for the pumped charge and spin in the regimes<br />
of small and large driving amplitude are provided for arbitrary bias. In the<br />
absence of a magnetic field, we obtain a striking, simple relation between<br />
the pumped charge at zero bias and at bias equal to the Coulomb charging<br />
energy. At finite magnetic field, interaction-induced pure spin pumping is<br />
shown to be possible at this finite bias value, and additional features appear<br />
in the pumped charge. For large-amplitude adiabatic driving, the magnitude<br />
of both the pumped charge and spin at the various resonances saturate at<br />
values which are independent of the specific shape of the pumping cycle.<br />
Each of these values provide an independent, quantitative measurement of<br />
the junction asymmetry.<br />
75
Posters Tuesday February 5<br />
Poster 27:<br />
Adiabatic pumping through an interacting quantum dot with spin-orbit coupling<br />
Stephan Rojek<br />
We study adiabatic pumping through a two-level quantum dot coupled to two<br />
normal metallic leads in the presence of spin-orbit coupling.[1] The variation<br />
of the two energy levels of the dot periodically in time leads to finite charge<br />
and spin currents.<br />
We calculate the pumped charge and spin using a diagrammatic real-time<br />
approach.[2] Going beyond the limit of noninteracting electrons on the<br />
quantum dot,[3] we study the situation of strong Coulomb interaction. In<br />
both limits of noninteracting and strongly interacting electrons, spin-orbit<br />
coupling provides the possibility for pure spin current. We introduce an<br />
isospin to describe the level degree of freedom. This isospin feels an exchange<br />
field similar to the exchange field in a quantum-dot spin valve. The exchange<br />
field originates form the Coulomb interaction and its strength is sensitive<br />
to the symmetry in the tunneling matrix elements. New features concerning<br />
the pure spin pumping as well as the absolute pumped charge of the two-level<br />
quantum dot with spin-orbit coupling arises from the Coulomb interaction.<br />
[1] S. Rojek, J. König, and A. Shnirman, arXiv: 1209.4770v1 (2012)<br />
[2] J. Splettstoesser, M. Governale, J. König, and R. Fazio, Phys. Rev. B<br />
74, 085305 (2006).<br />
[3] V. Brosco, M. Jerger, P. San-José, G. Zaránd, A. Shnirman, and G.<br />
Schön, Phys. Rev. B 82, 041309(R) (2010).<br />
Coauthors<br />
Jürgen König and Alexan<strong>der</strong> Shnirman<br />
76
Posters Tuesday February 5<br />
Poster 28:<br />
Explicit staggered grid finite difference scheme for (2+1)D Dirac fermions<br />
René Hammer<br />
We study the dynamics of Dirac fermion wave packets on magnetically structured<br />
surfaces of topological insulators and propose a gate-controlled Dirac<br />
fermion interferometer based on a solitonic domain wall structure which functions<br />
as a transistor. A preliminary summary of related work can be found<br />
online (arXiv:1205.6941). Work supported by FWF Project P21289-N16<br />
We discuss and compare several algorithms for a numerical solution of the<br />
time-dependent Dirac equation in 2 spatial dimensions which allow the use of<br />
a finite simulation region for open boundary situations. The newly proposed<br />
explicit finite difference schemes use space and time staggering of the grid,<br />
showing a computational complexity growing only linearly with the number<br />
of space-time grid-points. One of them preserves the linear dispersion relation<br />
of the Weyl equation for wave vectors aligned with the grid and yields only<br />
one additional Dirac cone. The second scheme leads to a purely monotonic<br />
free-particle dispersion avoiding an additional cone altogether. We discuss the<br />
energy dispersion relation, the proof of stability, a definition of the norm on<br />
the staggered grid, and the important issue of absorbing boundary conditions.<br />
These schemes are useful for numerical studies of Dirac fermions on topological<br />
insulators, where the surface state energy spectrum can be m! anipulat ed<br />
by perturbations which break time-reversal symmetry introducing an energy<br />
gap. Work supported by FWF Project P21289-N16<br />
René Hammer, Christian Ertler, and Walter Pötz<br />
Poster 29:<br />
Microwave-controlled manipulation of Majorana bound states<br />
Thomas Schmidt<br />
Majorana bound states have been proposed as building blocks for qubits on<br />
which certain operations can be performed in a topologically protected way<br />
using braiding. However, the set of these protected operations is not sufficient<br />
to realize universal quantum computing. We show that the electric field in<br />
a microwave cavity can induce Rabi oscillations between adjacent Majorana<br />
bound states. These oscillations can be used to implement an additional<br />
single-qubit gate. Supplemented with one braiding operation, this gate allows<br />
to perform arbitrary single-qubit operations.<br />
77
Posters Tuesday February 5<br />
Poster 30:<br />
Topological edge states in a HgTe quantum well in proximity to an s-wave<br />
superconductor<br />
Luzie Weithofer<br />
Topological insulators represent a new class of condensed matter systems<br />
which are characterized by topologically protected edge states. Two-dimensional<br />
topological insulators have been experimentally realized in HgTe<br />
quantum wells [1]. In a HgTe quantum well in the topologically non-trivial<br />
phase, two edge states of different spin propagate in opposite directions at<br />
the same boundary.<br />
Here, we consi<strong>der</strong> the proximity-induced superconductivity in the bulk of<br />
a HgTe quantum well in terms of a four-band model [2]. In addition, we<br />
include various symmetry-breaking terms and discuss their consequences on<br />
the topological properties of the system, focusing on the existence of edge<br />
states.<br />
[1] M. König et al., Science 318, 766 (2007) [2] B. Bernevig et al., Science<br />
314, 1757 (2006)<br />
Poster 31:<br />
z→−z Symmetry of Spin-Orbit Coupling and Weak Localization in Graphene<br />
Vladimir Falko<br />
We show that the influence of spin-orbit (SO) coupling on the weak-localization<br />
effect for electrons in graphene depends on the lack or presence of<br />
z→−z symmetry in the system. While, for z→−z asymmetric SO coupling,<br />
disor<strong>der</strong>ed graphene should display a weak antilocalization behavior at lowest<br />
temperature, z→−z symmetric coupling leads to an effective saturation of<br />
decoherence time which can be partially lifted by an in-plane magnetic field,<br />
thus tending to restore the weak-localization effect.<br />
78
Posters Tuesday February 5<br />
Poster 32:<br />
Intrinsic and substrate induced spin-orbit interaction in chirally stacked trilayer<br />
graphene<br />
Andor Kormanyos<br />
We present a combined group-theoretical and tight-binding approach to<br />
calculate the intrinsic spin-orbit coupling (SOC) in ABC stacked trilayer<br />
graphene. As a special case of our calculations we also consi<strong>der</strong> the intrinsic<br />
SOC in bilayer graphene. The comparison between our tight-binding bilayer<br />
results and the density functional computations of Konschuh et. al. allows<br />
us to estimate the values of the trilayer SOC parameters as well. We also<br />
discuss the situation when a substrate or adatoms induce strong SOC in<br />
only one of the layers of bilayer or ABC trilayer graphene. Both for the<br />
case of intrinsic and externally induced SOC we <strong>der</strong>ive effective Hamiltonians<br />
which describe the low-energy spin-orbit physics. We find that at the K point<br />
of the Brillouin zone the effect of Bychkov-Rashba type SOC is suppressed<br />
in bilayer and ABC trilayer graphene compared to monolayer graphene.<br />
Poster 33:<br />
Spin-orbit induced strong coupling of a single spin to a nanomechanical resonator<br />
Andras Palyi<br />
We theoretically investigate the spin-orbit-induced coupling of an electron<br />
spin to a bending vibrational mode in suspended carbon nanotube quantum<br />
dots. Our estimates indicate that, with current capabilities, a quantum dot<br />
with an odd number of electrons can serve as a realization of the Jaynes-<br />
Cummings model of quantum electrodynamics in the strong-coupling regime.<br />
A bending mode of the suspended tube plays the role of the optical mode and<br />
we identify two distinct two-level subspaces, at small and large magnetic field,<br />
which can be used as qubits in this setup. The strong intrinsic spin-mechanical<br />
coupling allows for detection, as well as manipulation of the spin qubit,<br />
and may yield enhanced performance of nanotubes in sensing applications.<br />
Reference:<br />
A. Palyi, P. R. Struck, M. Rudner, K. Flensberg and G. Burkard, Phys.<br />
Rev. Lett. 108, 206811 (2012)<br />
79
Posters Tuesday February 5<br />
Poster 34:<br />
Spin-orbit effects in electronic transport in DNA-CNT hybrids<br />
Sergio Ulloa<br />
We report on theoretical studies of electronic transport in the archetypical<br />
molecular hybrid formed by DNA wrapped around single-walled carbon<br />
nanotubes (CNTs). Using a Green’s function formalism in a π-orbital tightbinding<br />
representation, we investigate the role that spin-orbit interactions<br />
play on the CNT in the case of the helicoidal electric field induced by the<br />
polar nature of the adsorbed DNA molecule. We find that spin polarization<br />
of the current can take place in the absence of magnetic fields, depending<br />
strongly on the direction of the wrapping and length of the helicoidal field.<br />
These findings open new routes for using CNTs in spintronic devices.<br />
Poster 35:<br />
Covalent functionalization of carbon nanotubes with tetramanganese complexes<br />
Robert Frielinghaus<br />
We present first results on the covalent chemical functionalization of carbon<br />
nanotubes (CNTs) with polynuclear Mn 4 coordination complexes. Raman<br />
spectra give direct and indirect evidence of a successful reaction. It can only<br />
be achieved for tubes which contain defects with carboxylic groups. Changes<br />
in the magnetization behavior of the Mn 4 complexes due to the bonding<br />
to the CNTs are analyzed using data obtained in temperature-dependent<br />
SQUID measurements.<br />
These results are correlated with bright- and dark field high-resolution transmission<br />
electron microscopy measurements that show the repartition of the<br />
Mn 4 decoration on the CNTs. Its elemental analysis capabilities, energydispersive<br />
x-ray spectroscopy and electron energy loss spectroscopy, proof the<br />
existence of Mn on the CNTs. Investigating several oxidation strengths we<br />
can show that already a mild oxidation that leaves the nanotubes intact in<br />
terms of a finite electrical conductance is sufficient for functionalization. This<br />
is important for the future application of this material in transport devices.<br />
80
Posters Tuesday February 5<br />
Poster 36:<br />
Analysis of quantum transport features in complex carbon nanotube structures<br />
Robert Frielinghaus<br />
We have investigated two carbon nanotubes (CNTs) both in quantum transport<br />
and in the transmission electron microscope by means of a novel sample<br />
design. This enables us to determine the device structure unambiguously as<br />
a two-fold single-walled CNT bundle and an individual triple-walled CNT,<br />
respectively. The corresponding low-temperature transport experiments are,<br />
to our knowledge, the first ones unambiguously conducted on these very<br />
systems. The stability diagrams exhibit complex features as anti-crossings,<br />
Fano-shaped coulomb peaks, and regular sawtooth patterns. The origin of<br />
these features is only found with the detailed knowledge about the atomic<br />
structure, which cannot be obtained with standard sample layouts. More precisely,<br />
we measure capacitive and molecular interactions between the various<br />
elements of the devices and the environment.<br />
Poster 37:<br />
Nanomechanical read-out of a single spin<br />
Philipp Struck<br />
The spin of a single electron in a suspended carbon nanotube can be read<br />
out by using its coupling to the nano-mechanical motion of the nanotube. To<br />
show this, we consi<strong>der</strong> a single electron confined within a quantum dot formed<br />
by the suspended carbon nanotube. The spin- orbit interaction induces a<br />
coupling between the spin and one of the bending modes of the suspended<br />
part of the nanotube. We calculate the response of the system to pulsed<br />
external driving of the mechanical motion using a Jaynes-Cummings model.<br />
To account for resonator damping, we solve a quantum master equation, with<br />
parameters comparable to those used in recent experiments, and show how<br />
information of the spin state of the system can be acquired by measuring<br />
its mechanical motion. The latter can be detected by observing the current<br />
through a nearby charge detector.[1]<br />
[1] P. R. Struck, H. Wang, G. Burkard, arXiv:1212.1569<br />
81
Posters Tuesday February 5<br />
Poster 38:<br />
Cotunneling renormalization in carbon nanotube quantum dots<br />
Kirsanskas Gediminas<br />
We determine the level shifts induced by cotunneling in a Coulomb blockaded<br />
carbon nanotube quantum dot using leading-or<strong>der</strong> quasi-degenerate<br />
perturbation theory within a single nanotube “shell.” It is demonstrated<br />
that otherwise degenerate and equally tunnel coupled K and K’ states are<br />
mixed by cotunneling and therefore split up in energy except at the particle-hole<br />
symmetric midpoints of the Coulomb diamonds. In the presence<br />
of an external magnetic field, we show that cotunneling induces a gate dependent<br />
g-factor renormalization, and we outline different scenarios which might<br />
be observed experimentally, depending on the values of both intrinsic KK’-<br />
mixing and spin-orbit coupling.<br />
Poster 39:<br />
Kondo effect in graphene with Rashba spin-orbit coupling<br />
Diego Matrogiuseppe<br />
We study the effect of Rashba spin-orbit coupling in graphene with an<br />
adsorbed magnetic impurity. We model the system starting with a multiband<br />
An<strong>der</strong>son Hamiltonian, which is reduced to a single channel problem through<br />
suitable fermionic redefinitions. Then we map it to a Kondo Hamiltonian<br />
through a proper Schrieffer-Wolff transformation. The energy dependence<br />
of the Kondo exchange coupling follows the functional form of the density<br />
of states, giving rise to interesting phenomena as a function of the band filling.<br />
Compared to plain graphene, the presence of Rashba spin-orbit induces a<br />
finite density of states at the charge neutrality point. Therefore, a Kondo<br />
phase is expected for any finite value of the Rashba parameter, even for<br />
the particle-hole symmetric case. Finally, we compare these findings to recent<br />
results of magnetic impurities on bilayer graphene without spin-orbit coupling.<br />
Coauthors<br />
S. Ulloa and N. Sandler<br />
82
Posters Tuesday February 5<br />
Poster 40:<br />
Magnetic field effects on the finite-frequency noise and ac conductance of a<br />
Kondo quantum dot out of equilibrium<br />
Sarah Müller<br />
We present analytic results for the finite-frequency current noise and the<br />
nonequilibrium ac conductance for a Kondo quantum dot in presence of a<br />
magnetic field. We determine the line shape close to resonances and show<br />
that while all resonances in the ac conductance are broadened by the transverse<br />
spin relaxation rate; the noise at finite field additionally involves the<br />
longitudinal rate as well as sharp kinks resulting in singular <strong>der</strong>ivatives. Our<br />
results provide a consistent theoretical description of recent experimental<br />
data [Phys. Rev. Lett. 108, 046802 (2012)] for the emission noise at zero<br />
magnetic field, and we propose the extension to finite field for which we<br />
present a detailed prediction.<br />
Poster 41:<br />
Electron entanglement in Cooper pair beam splitter with magnetic fields<br />
Stephan Weiss<br />
We develop a theory that suggests the efficient manipulation of entangled<br />
electrons provided by a Cooper pair beam splitter. The splitting of coherent<br />
electrons forming a spin singlet is present if the superconductor is tunnel<br />
coupled to a double quantum dot [1]. In or<strong>der</strong> to probe entanglement, we<br />
allow for an inhomogeneous and, in general, non-collinear magnetic field in<br />
both dots. If the DQD-SC system is embedded in a transport setup, non-local<br />
current and noise properties are obtained within the real-time diagrammatic<br />
method [2]. As a small parameter we use the hybridization between splitter<br />
and normal leads. The tunnel coupling to the superconductor is taken into<br />
account non-perturbatively. Furthermore, we provide a detailed investigation<br />
of the violation of Bell’s inequality for various parameter regimes.<br />
[1] J. Eldridge, M. Governale, and J. König, Phys. Rev. B 82 184507, (2010).<br />
[2] M. Governale, M. Pala, and J. König, Phys. Rev. B 77 134513, (2008).<br />
83
Posters Tuesday February 5<br />
Poster 42:<br />
Current correlations in the interacting Cooper-pair beam-splitter<br />
Jerome Rech<br />
We propose an approach allowing the computation of currents and their correlations<br />
in interacting multi-terminal mesoscopic systems involving quantum<br />
dots coupled to normal and/or superconducting leads [1]. The formalism<br />
relies on the expression of branching currents and noise crossed correlations in<br />
terms of one- and two-particle Green’s functions for the dots electrons, which<br />
are then evaluated self-consistently within a conserving approximation [2].<br />
We illustrate our method with the Cooper-pair beam-splitter setup recently<br />
proposed [3], which we model as a double quantum dot with weak interactions,<br />
connected to a superconducting lead and two normal ones. Our method<br />
not only enables us to take into account a local repulsive interaction on the<br />
dots, but also to study its competition with the direct tunneling between<br />
dots. Our results suggest that even a weak Coulomb repulsion tends to favor<br />
positive current cross correlations in the antisymmetric regime (where the<br />
dots have opposite energies with respect to the superconducting chemical<br />
potential).<br />
Poster 43:<br />
Controlling entanglement and spin-correlations in double quantum dots using<br />
non-equilibrium currents<br />
Carlos Busser<br />
We study the non-equilibrium dynamics in a parallel double-quantum dot<br />
structure induced by a large bias voltage. By applying both a magnetic flux<br />
and a voltage, it is possible to generate spin-spin-correlations between the two<br />
quantum dots, whose sign and absolute value can be controlled by changing<br />
the bias voltage. Our study is based on the An<strong>der</strong>son-impurity model and<br />
we use time-dependent density matrix renormalization group simulations to<br />
obtain currents and spin-correlations in the non-equilibrium regime.<br />
84
List of participants<br />
1. Yulieth Cristina Arango, Forschungszentrum Jülich, Germany<br />
y.arango@fz-juelich.de<br />
2. Christian Bartsch, TU Braunschweig, Braunschweig, Germany<br />
c.bartsch@tu-braunschweig.de<br />
3. Bernd Beschoten, <strong>RWTH</strong> <strong>Aachen</strong> University, <strong>Aachen</strong>, Germany<br />
bernd.beschoten@physik.rwth-aachen.de<br />
4. Stefan Blügel, Forschungszentrum Jülich, Germany<br />
s.bluegel@fz-juelich.de<br />
5. Aldo Brunetti, Heinrich Heine Univerität - Düsseldorf, Düsseldorf, Germany<br />
brunetti@thphy.uni-duesseldorf.de<br />
6. Carlos Busser, LMU Munich, Munich, Germany<br />
C.Buesser@physik.uni-muenchen.de<br />
7. Hernan Calvo, <strong>RWTH</strong> <strong>Aachen</strong> University, <strong>Aachen</strong>, Germany<br />
hcalvo@physik.rwth-aachen.de<br />
8. Theo Costi, Research Centre Jülich GmbH, Jülich, Germany<br />
t.costi@fz-juelich.de<br />
9. Silvano De Franceschi, CEA, Grenoble, France<br />
silvano.defranceschi@cea.fr<br />
10. Manuel dos Santos Dias, Forschungszentrum Jülich, Jülich, Germany<br />
m.dos.santos.dias@fz-juelich.de<br />
11. Reinhold Egger, Heinrich Heine Univerität- Düsseldorf, Düsseldorf, Germany<br />
egger@thphy.uni-duesseldorf.de<br />
12. Sigurdur I. Erlingsson, Reykjavik University, Reykjavik, Iceland<br />
sie@ru.is<br />
13. Vladimir Falko, Lancaster University, Lancaster, United Kingdom<br />
v.falko@lancaster.ac.uk<br />
14. Robert Frielinghaus, Forschungszentrum Jülich, Jülich, Germany<br />
r.frielinghaus@fz-juelich.de<br />
15. Robert Frielinghaus, Forschungszentrum Jülich, Jülich, Germany<br />
r.frielinghaus@fz-juelich.de<br />
16. Kirsanskas Gediminas, University of Copenhagen, Copenhagen, Denmark<br />
gedikirs@nano.ku.dk<br />
17. Thomas Gerster, Fz-Jülich, Jülich, Germany<br />
t.gerster@fz-juelich.de<br />
85
18. Domenico Giuliano, Universita‘ della Calabria - Italy, Rende, Italy<br />
domenico.giuliano@fis.unical.it<br />
19. Stephan Grap, <strong>RWTH</strong> <strong>Aachen</strong> University, <strong>Aachen</strong>, Germany<br />
stephan.grap@rwth-aachen.de<br />
20. Kasper Grove-Rasmussen, University of Copenhagen, Copenhagen, Denmark<br />
k_grove@fys.ku.dk<br />
21. Jan-Christian Gunia, Forschungszentrum Jülich, Germany<br />
j-c.gunia@fz-juelich.de<br />
22. René Hammer, University Graz, Graz, Austria<br />
rene.hammer@uni-graz.at<br />
23. Fe<strong>der</strong>ica Haupt, <strong>RWTH</strong> <strong>Aachen</strong> University, Germany<br />
fe<strong>der</strong>ica.haupt@gmail.com<br />
24. Sebastian Heedt, Forschungszentrum Jülich, Jülich, Germany<br />
s.heedt@fz-juelich.de<br />
25. Fabian Heidrich-Meisner, LMU Munich, Munich, Germany<br />
heidrich-meisner@lmu.de<br />
26. Stefan Heinze, University of Kiel, Kiel, Germany<br />
heinze@physik.uni-kiel.de<br />
27. Michael Hell, Research Center Jülich, Jülich, Germany<br />
m.hell@fz-juelich.de<br />
28. Carsten Honerkamp, <strong>RWTH</strong> <strong>Aachen</strong>, Germany,<br />
honerkamp@physik.rwth-aachen.de<br />
29. Christoph Hörig, <strong>RWTH</strong>, <strong>Aachen</strong>, German<br />
hoerig@physik.rwth-aachen.de<br />
30. Julen Ibanez, University of the Basque Country, Leioa (Bizkaia), Spain<br />
julen.ibanez@ehu.es<br />
31. Henrik Johannesson, University of Gothenburg, Gothenburg, Sweden<br />
henrik.johannesson@physics.gu.se<br />
32. Marvin Junk, <strong>RWTH</strong> <strong>Aachen</strong>, <strong>Aachen</strong>, Germany<br />
Marvin.Junk@rwth-aachen.de<br />
33. Pascal Kaienburg, <strong>RWTH</strong>, <strong>Aachen</strong>, Germany<br />
pascal.kaienburg@rwth-aachen.de<br />
34. Vladislav Kataev, IFW Dresden, Dresden, Germany<br />
v.kataev@ifw-dresden.de<br />
35. Michael Kinza, <strong>RWTH</strong> <strong>Aachen</strong> University, <strong>Aachen</strong>, Germany<br />
kinza@physik.rwth-aachen.de<br />
86
36. Jürgen König, University of Duisburg-Essen, Duisburg, Germany<br />
koenig@thp.uni-due.de<br />
37. Francois Konschelle, <strong>RWTH</strong> - <strong>Aachen</strong>, <strong>Aachen</strong>, Germany<br />
konschelle@physik.rwth-aachen.de<br />
38. Andor Kormanyos, University of Konstanz, Konstanz, Germany<br />
andor.kormanyos@uni-konstanz.de<br />
39. Martin Leijnse, Copenhagen University, Copenhagen, Denmark<br />
leijnse@fys.ku.dk<br />
40. Andrei Manolescu, Reykjavik University, Reykjavik, Iceland<br />
manoles@ru.is<br />
41. Charles Marcus, University of Copenhagen, Copenhagen, Denmark,<br />
marcus@nbi.dk<br />
42. Diego Matrogiuseppe, Ohio University, United States,<br />
mastrogiuseppe@ifir-conicet.gov.ar<br />
43. Volker Meden, <strong>RWTH</strong> <strong>Aachen</strong>, <strong>Aachen</strong>, Germany<br />
meden@physik.rwth-aachen.de<br />
44. Sebastian Mehl, Forschungszentrum Jülich, Jülich, Germany<br />
s.mehl@fz-juelich.de<br />
45. Lukas Merker, Forschungszentrum Jülich GmbH, Jülich, Germany<br />
l.merker@fz-juelich.de<br />
46. Maciej Misiorny, Forschungszentrum Jülich, Germany<br />
m.misiorny@fz-juelich.de<br />
47. Markus Morgenstern, <strong>RWTH</strong>, <strong>Aachen</strong>, Germany<br />
mmorgens@physik.rwth-aachen.de<br />
48. André Müller, <strong>RWTH</strong> <strong>Aachen</strong>, Germany<br />
andre.mueller@physik.rwth-aachen.de<br />
49. Sarah Müller, Universität Wien, Wien, Austria<br />
sarah.mueller@univie.ac.at<br />
50. Amin Naseri Jorshari, Heinrich Heine University, Dusseldorf, Germany<br />
nasseri.amin@gmaul.com<br />
51. Christoph Neumann, <strong>RWTH</strong> <strong>Aachen</strong>, <strong>Aachen</strong>, Germany<br />
christoph.neumann@rwth-aachen.de<br />
52. Hoa Nghiem, Forschungszentrum Jülich, Jülich, Germany<br />
h.nghiem@fz-juelich.de<br />
53. Christoph Ohm, <strong>RWTH</strong> <strong>Aachen</strong>, <strong>Aachen</strong>, Germany<br />
ohm@physik.rwth-aachen.de<br />
54. San<strong>der</strong> Otte, TU Delft, Delft, The Netherlands<br />
a.f.otte@tudelft.nl<br />
87
55. Jens Paaske, Copenhagen University, Copenhagen, Denmark<br />
paaske@nbi.ku.dk<br />
56. Andras Palyi, Eotvos University Budapest, Budapest, Hungary<br />
andraspalyi@caesar.elte.hu<br />
57. Mikhail Pletyukhov, <strong>RWTH</strong>, <strong>Aachen</strong>, Germany<br />
pletmikh@physik.rwth-aachen.de<br />
58. Vlad Pribiag, TU Delft, Delft, The Netherlands<br />
v.s.pribiag@tudelft.nl<br />
59. Benedikt Probst, TU Braunschweig, Braunschweig, Germany<br />
b.probst@tu-braunschweig.de<br />
60. Jerome Rech, Aix Marseille Université, Marseille, France<br />
jerome.rech@cpt.univ-mrs.fr<br />
61. Maria-Theresa Rie<strong>der</strong>, Freie Universität Berlin, Berlin, Germany<br />
rie<strong>der</strong>m@physik.fu-berlin.de<br />
62. Stephan Rojek, Universität Duisburg-Essen, Duisburg, Germany<br />
strojek@thp.uni-due.de<br />
63. Achim Rosch, University of Cologne, Cologne, Germany<br />
rosch@thp.uni-koeln.de<br />
64. Julia Samm, University of Basel, Basel, Switzerland<br />
julia.samm@unibas.ch<br />
65. Nancy Sandler, Freie Universitat/Ohio University, Berlin, Germany<br />
sandler@ohio.edu<br />
66. Roman Saptsov, Forschungszentrum Jülich, Jülich, Germany<br />
r.saptsov@fz-juelich.de<br />
67. Thomas Schäpers, Forschungszentrum Jülich and <strong>RWTH</strong> <strong>Aachen</strong>, Jülich,<br />
Germany<br />
th.schaepers@fz-juelich.de<br />
68. Thomas Schmidt, Universität Basel, Basel, Switzerland<br />
thomas.schmidt@unibas.ch<br />
69. Michael Schnee, Forschungszentrum Jülich, Jülich, Germany<br />
m.schnee@fz-juelich.de<br />
70. Herbert Schoeller, <strong>RWTH</strong> <strong>Aachen</strong> University, <strong>Aachen</strong>, Germany<br />
schoeller@physik.rwth-aachen.de<br />
71. Christian Schönenberger, University of Basel, Basel, Switzerland<br />
Christian.Schoenenberger@unibas.ch<br />
72. Llorens Serra, University of Balearic Islands, Palma de Mallorca, Spain<br />
llorens.serra@uib.es<br />
88
73. Janine Splettstoesser, <strong>RWTH</strong> <strong>Aachen</strong>, <strong>Aachen</strong>, Germany<br />
splett@physik.rwth-aachen.de<br />
74. Christoph Stampfer, <strong>RWTH</strong> <strong>Aachen</strong>, <strong>Aachen</strong>, Germany<br />
christoph@stampfer.com<br />
75. Philipp Stegmann, Universität Duisburg-Essen, Duisburg, Germany<br />
philipp.stegmann@uni-due.de<br />
76. Robin Steinigeweg, TU Braunschweig, Braunschweig, Germany<br />
robin@robin-st.de<br />
77. An<strong>der</strong>s Ström, TU Braunschweig, Braunschweig, Germany<br />
an<strong>der</strong>s.p.strom@gmail.com<br />
78. Philipp Struck, University of Konstanz, Konstanz, Germany<br />
philipp.struck@uni-konstanz.de<br />
79. Arturo Tagliacozzo, Universita’ di Napoli "Fe<strong>der</strong>ico II", Napoli , Italy<br />
arturo@na.infn.it<br />
80. Seigo Tarucha, University of Tokyo, Tokyo, Japan<br />
tarucha@ap.t.u-tokyo.ac.jp<br />
81. Jonckheere Thibaut, CNRS , Marseille, France<br />
thibaut.jonckheere@cpt.univ-mrs.fr<br />
82. Carsten Timm, Technische Universität Dresden, Dresden, Germany<br />
carsten.timm@tu-dresden.de<br />
83. Mircea Trif, UCLA, Los Angeles, United States<br />
mtrif@physics.ucla.edu<br />
84. Sergio Ulloa, Ohio University, Athens, Ohio, USA<br />
ulloa@ohio.edu<br />
85. Herre van <strong>der</strong> Zant, Delft University of Technology, Delft, The Netherlands<br />
h.s.j.van<strong>der</strong>zant@tudelft.nl<br />
86. Ilse van Weperen, Delft University of Technology, Delft, The Netherlands<br />
I.vanWeperen@tudelft.nl<br />
87. Christian Volk, <strong>RWTH</strong> <strong>Aachen</strong>, <strong>Aachen</strong>, Germany<br />
c.volk@fz-juelich.de<br />
88. Stephan Weiss, Universität Duisburg-Essen, Duisburg, Germany<br />
weiss@thp.uni-due.de<br />
89. Luzie Weithofer, TU Braunschweig, Braunschweig, Germany<br />
luzie.weithofer@tu-bs.de<br />
90. Ireneusz Weymann, Adam Mickiewicz University, Poznan, Poland<br />
weymann@amu.edu.pl<br />
89