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关于举办《Topological insulators,quantum hall effects and disorder》学术报告的通知

发布日期:2017-04-25 10:28      来源:未知      点击:
  为提高学术氛围,开阔学校师生的视野,促进学术交流,校科协联合国际教育学院、理学院邀请到法国马塞大学Laurent RAYMOND教授举办学术报告,欢迎广大师生踊跃参加!
  时 间:2017年4月26日 14:00-15:00
  地 点:综合楼A301
  题 目:Topological insulators,quantum hall effects and disorder
  报告人:Laurent RAYMOND教授
  承办单位:理学院
 
 
 
ABSTRACT
 
  Spin Hall effects are phenomena where electrical currents are related to spin currents  or spin-polarized charge currents. For this reason, they are key phenomena in the field of spintronics, both as a way to generate, and to detect spin currents. In particular the use of topological insulators seems to be a promising way to obtain devices based on the quantum spin Hall effect, in which the system is essentially an insulator with 4 (2 conducting when polarized) dissipationless conducting helical edge states, robust to perturbations that preserve the time reversal symmetry.
 
  Recently, it has been experimentally demonstrated that a 2D topological insulator, can be modified by a doping with magnetic impurities (not time-reversal preserving)to obtain the so-called Quantum Anomalous Hall effect (or a Chern insulator state), in which the charge conduction on an edge channel, is dependent on the carrier’s spin, leading to a spin-polarization dependent transport as in a Quantum spin Hall effect, but without external magnetic field.
 
  After a brief review of some of the spin Hall effects properties, we will present a theoretical work in which
we show that a two-dimensional topological insulator doped with magnetic impurities undergoes a disorder driven quantum phase transition between three topologically different states, when the disorder strength is varied. Namely, topological insulator, Chern insulator and conventional insulator state.
 
  We start by studying a model of a HgTe quantum well, with uniformly distributed magnetic moments polarized perpendicularly to the plane. Numerical transport calculations were performed using the Landauer formula. We investigate the conductance in a two terminals setup, as a function of the disorder strength and the chemical potential. We focused in particular on the behavior of the edge channels according to their spin. Finally, we calculate, in the second order self-consistent Born approximation, the real part of the self-energy to obtain explicit expressions of the renormalized mass and the chemical potential.