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Abstract
The quantum geometric tensor is a physical quantity related to the quantum distance between nearby quantum states. The imaginary part of this quantum geometric tensor is the well-known Berry curvature responsible for the anomalous Hall effects. Less known is the real part of the quantum geometric tensor, called the quantum metric. It has been increasingly recognized that the quantum metric tensor plays a key role in understanding a material’s fundamental characteristics, such as optical responses, nonlinear Hall effects, electron-phonon coupling, and superconductivity. In this talk, I will introduce our latest results on the direct measurement of the quantum metric tensor in one of the elemental layered materials, black phosphorus1. Using angle-resolved photoemission spectroscopy (ARPES) and synchrotron radiation, we measured the polarization dependence of ARPES intensity in the valence band of black phosphorus, providing us with information on the full pseudospin texture². It could be used to extract the complete quantum metric tensor and their k distributions3. If time permits, I will also discuss how this measurement of the full quantum phases can be extended to the case of systems with two pairs of sublattices, especially in terms of ARPES dark states4.
References:
1. J. Kim et al., Science 349, 723 (2015).
2. S. W. Jung et al., Nature Mater. 19, 277 (2020).
3. S. Kim et al., Science 388, 1050 (2025).
4. Y. Chung et al., Nature Phys. 20, 1582 (2024).
Bio
Keun Su Kim is an Underwood Distinguished Professor in Yonsei University, South Korea. After getting his Ph. D in Yonsei University, he came to the Lawrence Berkeley National Laboratory as a postdoctoral researcher working with Eli Rotenberg and Aaron Bostwick. Ever since he started his independent research group 2014, he has focused on the study of black phosphorus. Last year, he visited Zhi-Xun Shen’s group, Stanford University, and is currently an active user of ARPES beamlines in both ALS and SSRL.
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