nanoelectronics - Institut d'Études Scientifiques de Cargèse (IESC)
nanoelectronics - Institut d'Études Scientifiques de Cargèse (IESC) nanoelectronics - Institut d'Études Scientifiques de Cargèse (IESC)
Friday Friday, October 2 Metallic phase of the quantum Hall effect in four-dimensional space Jonathan M. Edge, J. Tworzydlo, C. W. J. Beenakker Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, Hoza 69, 00--681 Warsaw, Poland We study the phase diagram of the quantum Hall effect in four-dimensional (4D) space [1]. Unlike in 2D, in 4D there exists a metallic as well as an insulating phase, depending on the disorder strength. The critical exponent ≈ 1.2 of the diverging localization length at the quantum Hall insulator-to-metal transition differs from the semiclassical value = 1 of 4D Anderson transitions in the presence of time-reversal symmetry. Our numerical analysis is based on a mapping of the 4D Hamiltonian onto a 1D dynamical system, providing a route towards the experimental realization of the 4D quantum Hall effect. [1] J.M. Edge, J. Tworzydlo, C. W. J. Beenakker Metallic phase of the quantum Hall effect in four-dimensional space arXiv:1206.0099 to be published in PRL (2012) __________________________________________________________________________ Thermal metal in topological superconductors Jakub Tworzydlo (1) , I. C. Fulga (2) , A. R. Akhmerov (2) , C.W.J. Beenakker (2) , B. Beri (3) (1) Faculty of Physics, University of Warsaw, Poland (2) Instituut-Lorentz, Universiteit Leiden, The Netherlands (3) TCM Group, Cavendish Laboratory, United Kingdom The thermal quantum Hall effect appears in the absence of time-reversal symmetry in a single layer of a chiral p-wave superconductor. The insulator-insulator transition associated with this effect is generically present only for weak disorder. For stronger disorder we find a transition to a delocalized phase, known as the thermal metal. In contrast, for a helical superconductor in the presence of time-reversal symmetry the transition between two topologically distinct thermal insulators occurs via the intervening thermal metal phase, even for an arbitrarily weak disorder. We present a detailed study of a phase diagram and the critical exponents for these topologically induced transitions. We also point to an underling mechanism of Majorana states formation in both chiral and helical systems. [1] I. C. Fulga, A. R. Akhmerov, J. Tworzydlo, B. Beri, and C. W. J. Beenakker, Phys. Rev. B 86, 054505 (2012) [2] M. V. Medvedyeva, J. Tworzydlo, and C. W. J. Beenakker, Phys. Rev. B 81, 214203 (2010) [3] J. H. Bardarson, M. V. Medvedyeva, J. Tworzydło, A. R. Akhmerov, and C. W. J. Beenakker, Phys.Rev. B 81, 121414(R) (2010) [4] M. Wimmer, A. R. Akhmerov, M. V. Medvedyeva, J. Tworzydlo, C. W. J. Beenakker, Phys. Rev. Lett. 105, 046803 (2010)
Friday Nanoscale inhomogeneities in diluted magnetic systems : Effects on Curie temperature and spontaneous magnetization Akash Chakraborty (1,2) , Richard Bouzerar (3) , Paul Wenk (4) , Stefan Kettemann (2,5) , and Georges Bouzerar (3,2) (1) Karlsruhe Institute of Technology, 76128 Karlsruhe, Germany (2) Jacobs University Bremen, 28759 Bremen, Germany (3) Institut Néel, CNRS, 38042 Grenoble Cedex 09, France (4) Universitaet Regensburg, 93040 Regensburg, Germany (5) Pohang University of Science and Technology (POSTECH), Pohang 790-784, South Korea The presence of nanoscale inhomogeneities has been experimentally evidenced in several diluted magnetic systems, which in turn often leads to interesting physical phenomena. Among them room-temperature ferromagnetism is one of the most interesting and sought after topics in today’s emerging field of spintronics. However, until now, in the dilute regime it has been difficult to obtain Curie temperatures larger than that measured in well annealed samples of (Ga,Mn)As (∼190K for 12% doping). Here we suggest an innovative path to roomtemperature ferromagnetism in diluted magnetic semiconductors. We theoretically show that even a small concentration of nanoscale inhomogeneities can result in a gigantic increase of the critical temperatures [1]. We give a plausible explanation for the wide variation of the critical temperatures measured in (Ga,Mn)N and provide a better understanding of the likely origin of very high Curie temperatures measured occasionally. We also show that nano-sized clusters of magnetic impurities can lead to drastic effects on the temperature dependent magnetization compared to that of homogeneously diluted compounds [2]. The unusual and unconventional nature of the magnetization curves is found to strongly depend on the relative concentration of the inhomogeneities as well as the effective range of the exchange interactions. [1] A. Chakraborty, R. Bouzerar, S. Kettemann, and G. Bouzerar, Nanoscale inhomogeneities: A new path toward high Curie temperature ferromagnetism in diluted materials, Phys. Rev. B 85 014201 (2012). [2] A. Chakraborty, P. Wenk, R. Bouzerar, and G. Bouzerar, Spontaneous magnetizationin in presence of nanoscale inhomogeneities in diluted magnetic systems, (submitted to Phys. Rev. B). __________________________________________________________________________ Onsager relations in a two-dimensional electron gas with spin-orbit coupling Roberto Raimondi, Cosimo Gorini, and Peter Schwab CNISM and Dipartimento di Fisica "E. Amaldi", via della Vasca Navale 84, Università Roma Tre, 00146 Roma, Italy Institut de Physique et Chimie des Matériaux de Strasbourg (UMR 7504), CNRS and Université de Strasbourg, 23 rue du Loess, BP 43, F-67034 Strasbourg Cedex 2, France Institut für Physik, Universität Augsburg, 86135 Augsburg, Germany Theory predicts for the two-dimensional electrons gas with only Rashba spin-orbit interaction a vanishing spin Hall conductivity and at the same time a finite inverse spin Hall effect. We show how these seemingly contradictory results are compatible with the Onsager relations: the latter do hold for spin and particle (charge) currents in the two-dimensional electron gas, although (i) their form depends on the experimental setup and (ii) a vanishing bulk spin Hall
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- Page 15 and 16: Tuesday Electron refrigeration by n
- Page 17 and 18: Wednesday [4] K. Saito, G. Benenti,
- Page 19 and 20: Thursday [3] B. A. Bernevig, T. L.
- Page 21: Thursday Electronic standing waves
- Page 25 and 26: Friday Electron focusing in graphem
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Friday<br />
Nanoscale inhomogeneities in diluted magnetic systems : Effects on Curie<br />
temperature and spontaneous magnetization<br />
Akash Chakraborty (1,2) , Richard Bouzerar (3) , Paul Wenk (4) , Stefan Kettemann (2,5) , and<br />
Georges Bouzerar (3,2)<br />
(1)<br />
Karlsruhe <strong>Institut</strong>e of Technology, 76128 Karlsruhe, Germany<br />
(2)<br />
Jacobs University Bremen, 28759 Bremen, Germany<br />
(3)<br />
<strong>Institut</strong> Néel, CNRS, 38042 Grenoble Ce<strong>de</strong>x 09, France<br />
(4)<br />
Universitaet Regensburg, 93040 Regensburg, Germany<br />
(5)<br />
Pohang University of Science and Technology (POSTECH), Pohang 790-784, South<br />
Korea<br />
The presence of nanoscale inhomogeneities has been experimentally evi<strong>de</strong>nced in several<br />
diluted magnetic systems, which in turn often leads to interesting physical phenomena.<br />
Among them room-temperature ferromagnetism is one of the most interesting and sought<br />
after topics in today’s emerging field of spintronics. However, until now, in the dilute regime it<br />
has been difficult to obtain Curie temperatures larger than that measured in well annealed<br />
samples of (Ga,Mn)As (∼190K for 12% doping). Here we suggest an innovative path to roomtemperature<br />
ferromagnetism in diluted magnetic semiconductors. We theoretically show that<br />
even a small concentration of nanoscale inhomogeneities can result in a gigantic increase of<br />
the critical temperatures [1]. We give a plausible explanation for the wi<strong>de</strong> variation of the<br />
critical temperatures measured in (Ga,Mn)N and provi<strong>de</strong> a better un<strong>de</strong>rstanding of the likely<br />
origin of very high Curie temperatures measured occasionally. We also show that nano-sized<br />
clusters of magnetic impurities can lead to drastic effects on the temperature <strong>de</strong>pen<strong>de</strong>nt<br />
magnetization compared to that of homogeneously diluted compounds [2]. The unusual and<br />
unconventional nature of the magnetization curves is found to strongly <strong>de</strong>pend on the relative<br />
concentration of the inhomogeneities as well as the effective range of the exchange<br />
interactions.<br />
[1] A. Chakraborty, R. Bouzerar, S. Kettemann, and G. Bouzerar, Nanoscale<br />
inhomogeneities: A new path toward high Curie temperature ferromagnetism in diluted<br />
materials, Phys. Rev. B 85 014201 (2012).<br />
[2] A. Chakraborty, P. Wenk, R. Bouzerar, and G. Bouzerar, Spontaneous magnetizationin in<br />
presence of nanoscale inhomogeneities in diluted magnetic systems, (submitted to Phys.<br />
Rev. B).<br />
__________________________________________________________________________<br />
Onsager relations in a two-dimensional electron gas with spin-orbit coupling<br />
Roberto Raimondi, Cosimo Gorini, and Peter Schwab<br />
CNISM and Dipartimento di Fisica "E. Amaldi", via <strong>de</strong>lla Vasca Navale 84, Università Roma<br />
Tre, 00146 Roma, Italy<br />
<strong>Institut</strong> <strong>de</strong> Physique et Chimie <strong>de</strong>s Matériaux <strong>de</strong> Strasbourg (UMR 7504), CNRS and<br />
Université <strong>de</strong> Strasbourg, 23 rue du Loess, BP 43, F-67034 Strasbourg Ce<strong>de</strong>x 2, France<br />
<strong>Institut</strong> für Physik, Universität Augsburg, 86135 Augsburg, Germany<br />
Theory predicts for the two-dimensional electrons gas with only Rashba spin-orbit interaction<br />
a vanishing spin Hall conductivity and at the same time a finite inverse spin Hall effect. We<br />
show how these seemingly contradictory results are compatible with the Onsager relations:<br />
the latter do hold for spin and particle (charge) currents in the two-dimensional electron gas,<br />
although (i) their form <strong>de</strong>pends on the experimental setup and (ii) a vanishing bulk spin Hall
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