报告人题目：Novel Metal-Insulator Transitions in 2D Electron Gases

报告人：  王向荣 教授（香港科技大学）

报告时间：2019 年 12 月 27 日（周五）14：00 -- 15：00

报告地点：北洋园校区 32 教 218 室

报告人摘要：

In this talk, I will start with the conventional wisdom of the Anderson localization transitions.  Namely, all systems can be classified into three ensembles: the Gaussian orthogonal ensembles (GOE) when a system has both time-reversal and spin-rotational symmetries; the Gaussian unitary ensembles (GUE) when a system has neither time-reversal nor spin-rotational symmetries; and the Gaussian symplectic ensembles (GSE) when a system has time-reversal symmetry, but without spin-rotational symmetry. At the critical dimension of 2, no extended states exist in GOE at an arbitrary weak disorder, and extended states could exist in a GSE or a GUE when a strong perpendicular magnetic field is applied to drive the system into quantum Hall region. Then I will argue the intrinsic inconsistency of this standard picture.  It turns out that spin-orbit interactions play a crucial role. The types of Anderson-localization transitions (metal-insulator transitions) in a two-dimensional system are sensitive to the types and strength of spin-orbit interactions. I will present several simple models that support Berezinskii-Kosterlitz-Thouless type transition from a band of localized states to a band of critical states; or a Berezinskii-Kosterlitz-Thouless type transition from a band of conventional extended states to a band of critical states. In contrast to the conventional wisdom, I will also provide the evidences that support the existence of extended states in a GUE at a weak magnetic field.

This work is supported by the National Natural Science Foundation of China (Grants No. 11774296 and 1974296) and Hong Kong RGC (Grants No. 16301518, 16301619 and 16300117).

报告人简介：王向荣，香港科技大学终身教授；1984年毕业于武汉大学物理系；1990年在美国罗彻斯特大学(University of Rochester)获博士学位。研究方向：凝聚态理论，研究领域包括量子霍尔效应，金属-绝缘体相变，超晶格以及磁动力学中；迄今已在国际权威学术杂志发表论文过百篇。