Coherent spin control and geometrical phases in mesoscopic conductors

• Applicant: Professor Dr. Klaus Richter
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2010 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 164558368

• Final Report Year: 2017

Final Report Abstract

The project has been embedded within the German-Japanese Research Unit FOR 1483 entitled “Topological Electronics”. As a major common research direction within this framework the role of charge carrier spin (and associated topological phases) on electrical transport has been considered both, for so-called topological insulators and systems with strong spin-orbit coupling. The present theory project has successfully contributed to both of these research branches. On the one hand, in close cooperation with various German and Japanese experimental groups of the consortiuum, we considered topological effects of spin on coherent charge transport in lowdimensional conductors characterized by strong spin-orbit coupling. This included the use of a spin-geometric, Berry phase to steer the conductance through semiconductor quantum rings for the first time, the realization of a so-called persistent spin-helix state allowing for the first allelectrical determination of spin-orbit coupling coefficients, and finally providing a proof-of-principle for a spin transistor function, based on controlled spin-dynamics in helical external magnetic fields. On the other hand, we developed theoretical models for quantized charge transport along the edges of two-dimensional topological insulators. In an ideal situation these edge modes should provide reflectionless transport that, however, is difficult to achieve in experiment. Based on numerical transport calculations we considered the effect of dephasing mechanisms at finite temperature and due to magnetic fields. Finally, we proposed yet another spin transistor action using constrictions in topological insulators to switch charges and spin between different topological insulator edge states. The research has contributed to 13 publications in refereed journals.

Publications

• Switching Spin and Charge between Edge States in Topological Insulator Constrictions, Phys. Rev. Lett. 107, 086803 (2011)
  V. Krueckl and K. Richter
  
• Weak localization in mesoscopic hole transport: Berry phases and classical correlations, Phys. Rev. Lett. 106, 146801 (2011)
  V. Krueckl, M. Wimmer, I. Adagideli, J. Kuipers and K. Richter
  
• Gate-controlled persistent spin helix state in (In,Ga)As quantum wells, Phys. Rev. B 8, 081306 (2012)
  M. Kohda, V. Lechner, Y. Kunihashi, T. Dollinger, P. Olbrich, C. Schönhuber, I. Caspers, V. Belkov, L. Golub, D. Weiss, K. Richter, J. Nitta and S. Ganichev
  
• Probing the Band Topology of Mercury Telluride through Weak Localization and Antilocalization, Semiconductor Science and Technology 27, 124006 (2012)
  V. Krueckl and K. Richter
  
• Spin-Transistor Action via Tunable Landau-Zener Transitions, Science 337, 324-327 (2012)
  C. Betthausen, T. Dollinger, H. Saarikoski, V. Kolkovsky, G. Karczewski, T. Wojtowicz, K. Richter and D. Weiss
  
• The ABC of Aharonov Effects, Physics 5, 22 (2012)
  K. Richter
  
• Control of the spin geometric phase in semiconductor quantum rings, Nature Communications 4 (2013)
  F. Nagasawa, D. Frustaglia, H. Saarikoski, K. Richter and J. Nitta
  
• Direct determination of spin-orbit interaction coefficients and realization of the persistent spin helix symmetry, Nature Nanotechnology 9, 703-709 (2014)
  A. Sasaki, S. Nonaka, Y. Kunihashi, M. Kohda, T. Bauernfeind, T. Dollinger, K. Richter and J. Nitta
  
• Using Topological Insulator Proximity to Generate Perfectly Conducting Channels in Materials without Topological Protection, New Journal of Physics 16, 113058 (2014)
  S. Essert, V. Krueckl and K. Richter
  
• Magnetotransport in disordered two-dimensional topological insulators: signatures of charge puddles, 2D Materials 2, 024005 (2015)
  S. Essert and K. Richter