Novel metal-insulator transitions in disordered two-dimensional systems

报告题目：Novel metal-insulator transitions in disordered two-dimensional systems

报告人：汪 晨 电子科技大学电子科学与工程学院 cwangad@connect.ust.hk

报告时间：2019年9月12日　上午 10:00-11:00

报告邀请人：陈垂针

报告地点：物理科技楼101室

报告摘要：Disorders are ever-present. The disorder-induced quantum phase transitions from extended states to localized states, known as the Anderson localization transitions, have been of fundamental importance in modern condensed matter physics after P. W. Anderson published his groundbreaking work in 1958. For noninteracting closed Schrodinger systems, it is well-established that Anderson localization transitions exist (do not exist) in one-dimensional (three-dimensional) disordered systems. However, whether Anderson localization transitions are allowed in the critical dimension, i.e., two-dimension, has not yet been conclusive, which has also been drawn increasing attention in recent years.In this talk, I will briefly discuss some current progress concerning the above issue.

The well-established one-parameter scaling theory predicts that all states are localized in two-dimensional systems except for those with time-reversal symmetry and spin-orbit coupling. However, our numerical calculations show that extended states appear in systems without time-reversal symmetry (even at extremely weak magnetic fields) as well. More strikingly, the form of metal-insulator transitions depends on the form of spin-orbit interactions: conventional Anderson localization transitions for uniform spin-orbit couplings but Berezinskii-Kosterlitz-Thouless transitions for random spin-orbit couplings. In some specific systems, novel quantum phase transitions from diffusive metals to marginal metals, then to Anderson insulators is observed.

References:

[1] Anti-levitation in integer quantum Hall systems, C. Wang, Y. Avishai, Yigal Meir, and X. R. Wang, Phys. Rev. B 89, 045314 (2014).

[2] Band of Critical States in Anderson Localization in a Strong Magnetic Field with Random Spin-Orbit Scattering, C. Wang, Ying Su, Y. Avishai, Yigal Meir, and X. R. Wang, Phys. Rev. Lett. 114, 096803 (2015).

[3] Absence of localization in disordered two-dimensional electron gas at weak magnetic field and strong spin-orbit coupling, Ying Su, C. Wang, Y. Avishai, Yigal Meir, and X. R. Wang, Sci. Rep. 6, 33304 (2016).

[3] Anderson transition of two-dimensional spinful electrons in the Gaussian unitary ensemble. C. Wang and X. R. Wang, Phys. Rev. B 96, 104204 (2017).

[4] Unusual Metal to Marginal-Metal Transition in Two-Dimensional Ferromagnetic Electron Gases, Weiwei Chen, C. Wang, Qinwei Shi, Quanxiang Li, and X. R. Wang, arXiv:1907.12213.

报告人简介：报告人汪晨于2011年9月获得武汉大学物理学学士学位并于2016年11月获得香港科技大学哲学博士（物理学）学位。在获得博士学位后，报告人加入电子科技大学电子科学与工程学院从事博士后研究。报告人的研究方向主要包括传统二维系统和拓扑系统的安德森无序相变和自旋电子学。