报告题目：New insights on Anderson localization problems in non-Hermitian systems

报告人：汪晨 副教授（天津大学量子交叉研究中心）

报告时间：2025年6月19日（周四）14：00-15：30

报告地点：北洋园校区49教210室

报告摘要：

The Anderson localization transition, which marks the shift from extended to localized states due to disorder, is a fundamental issue in wave physics. Although this phenomenon has been extensively studied in closed systems described by Hermitian Hamiltonians, the understanding of localization in disordered systems is still incomplete. Disordered non-Hermitian systems present many unique localization phenomena that differ from their Hermitian counterparts, and I will briefly discuss some relevant new findings in this talk.

First, I will explore the Anderson localization problem in a disordered two-dimensional system influenced by complex on-site energy, introducing the concept of the mobility boundary. Notably, the level statistics of the extended states in such systems follow a Poisson distribution, contrasting with the Wigner-Dyson distribution observed in the Hermitian case.

Next, I will present new results regarding non-Hermitian disordered systems featuring exceptional points. Near these exceptional points, the nearest-neighbor level spacing distribution exhibits linear repulsion, and the criticality of the Anderson localization transition belongs to a superuniversality class.

Third, I will discuss a novel type of localization-localization transition occurring in disordered non-Hermitian two-dimensional quantized quadrupole insulators, which resembles a Berezinskii-Kosterlitz-Thouless transition.

Finally, I will focus on a specific category of non-Hermitian systems known as nonreciprocal systems, where we will demonstrate the validity of the one-parameter scaling hypothesis, irrespective of symmetry and dimensionality.

报告人简介：

汪晨，天津大学理学院物理系副教授。其主要研究方向包括拓扑相变、自旋电子学以及安德森局域化问题。目前，汪晨的研究兴趣关注于如何表征非互易系统中的安德森相变以及可能出现的新奇量子态和自旋系统中的拓扑孤子、自旋波和拓扑系统的相互作用等问题。

参考文献：

[1] C. Wang and X. R. Wang, Level statistics of extended states in random non-Hermitian Hamiltonians, Phys. Rev. B 101, 165114 (2020).

[2] C. Wang and X. R. Wang, Linear level repulsions near exceptional points of non-Hermitian systems, Phys. Rev. B 106, L081118 (2022).

[3] C. Wang and X. R. Wang, Anderson localization transitions in disordered non-Hermitian systems with exceptional points, Phys. Rev. B 107, 024202 (2023).

[4] C. Wang, W. He, H. Ren, and X. R. Wang, Berezinskii-Kosterlitz-Thouless-like localization-localization transitions in disordered two-dimensional quantized quadrupole insulators, Phys. Rev. B 109, L020202 (2024).

[5] C. Wang, W. He, X. R. Wang, and H. Ren, Unified one-parameter scaling function for Anderson localization transitions in non-reciprocal non-Hermitian systems, Phys. Rev. Lett. 134, 176301 (2025).

[6] C. Wang, W. He, X. R. Wang, and H. Ren, One-parameter scaling function for Anderson localization transitions in high-dimensional lattices with non-reciprocity, in preparation.