第8回物理工学科教室談話会[Prof. Bohm-Jung Yang・10/21(火)14:00～]

講　師：Prof. Bohm-Jung Yang
所　属：Seoul National University
題　目：How to measure the quantum geometry of Bloch electrons in solids?
日　時：2025 年 10 月 21 日(火)14:00～
Date and Time： October 21th, 2025 (Tuesday) 14:00-
場　所：工 6 号館 3 階セミナー室 A
Place：Seminar Room A, 3rd floor, Engineering Bldg. 6

Abstract：
Understanding the geometric properties of quantum states and their implications in fundamental physical phenomena is at the core of modern physics. The Quantum Geometric Tensor (QGT) is a central physical object in this regard, encoding complete information about the geometry of the quantum state. The imaginary part of the QGT is the well-known Berry curvature, which plays a fundamental role in the topological magnetoelectric and optoelectronic phenomena. The real part of the QGT is the quantum metric, whose importance has come to prominence very recently, giving rise to a new set of quantum geometric phenomena, such as anomalous Landau levels, flat band superfluidity, excitonic Lamb shifts, and nonlinear Hall effect. Despite the central importance of the QGT, its experimental measurements have been restricted only to artificial two-level systems. In this talk, I am going to present two recent progresses in the QGT measurement of Bloch states in solids. First, I will propose a general method to extract the QGT by introducing another geometrical tensor, the quasi-QGT, whose components, the band Drude weight and orbital angular momentum, are experimentally accessible and can be used for extracting the QGT [1]. In the second part, I will report the first direct measurement of the full quantum metric tensors using black phosphorus as a representative material [2]. The key idea is to extract the momentum space distribution of the pseudospin texture of the valence band from the polarization dependence of angle-resolved photoemission spectroscopy measurement.

[1] M. Kang et al., Nature Physics 21, 110-117 (2025). [2] S. Kim et al., Science. 388, 1050-1054 (2025).

紹介教員：森本 高裕 准教授（物理工学専攻）、村上 修一 教授（物理工学専攻）