近日，美国麻省理工学院的Riccardo Comin与韩国首尔国立大学的Bohm-Jung Yang等人合作，实现了固体中量子几何张量的测量。相关研究成果已于2024年11月25日在国际知名学术期刊《自然—物理学》上发表。
本研究开发了一种利用极化、自旋和角度分辨光电子能谱在晶体固体中，测量量子几何张量（QGT）的方法框架。利用这一框架，研究人员成功地在具有拓扑平带的笼目金属 CoSn 中有效重构了 QGT。这一动量分辨和能量分辨的 QGT 光谱探测技术的建立，有望极大地推动研究人员对广泛晶体系统中量子几何响应的理解。
据悉，理解量子态的几何性质及其在基本物理现象中的影响，是当代物理学的核心内容之一。量子几何张量（QGT）在这方面是一个核心物理对象，它编码了关于量子态几何结构的完整信息。QGT的虚部是众所周知的贝里曲率，它在拓扑磁电和光电子现象中发挥着不可或缺的作用。
QGT的实部是量子度量，其重要性近年来日益凸显，引发了一系列新的量子几何现象，如反常朗道能级、平带超流动性、激子兰姆位移和非线性霍尔效应。尽管QGT具有核心重要性，但其实验测量一直仅限于人工二能级系统。
附：英文原文
Title: Measurements of the quantum geometric tensor in solids
Author: Kang, Mingu, Kim, Sunje, Qian, Yuting, Neves, Paul M., Ye, Linda, Jung, Junseo, Puntel, Denny, Mazzola, Federico, Fang, Shiang, Jozwiak, Chris, Bostwick, Aaron, Rotenberg, Eli, Fuji, Jun, Vobornik, Ivana, Park, Jae-Hoon, Checkelsky, Joseph G., Yang, Bohm-Jung, Comin, Riccardo
Issue&Volume: 2024-11-25
Abstract: Understanding the geometric properties of quantum states and their implications in fundamental physical phenomena is a core aspect of contemporary 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 an integral role in the topological magnetoelectric and optoelectronic phenomena. The real part of the QGT is the quantum metric, whose importance has come to prominence 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. Here, we develop a framework to measure the QGT in crystalline solids using polarization-, spin- and angle-resolved photoemission spectroscopy. Using this framework, we demonstrate the effective reconstruction of the QGT in the kagome metal CoSn, which hosts topological flat bands. Establishing this momentum- and energy-resolved spectroscopic probe of the QGT is poised to significantly advance our understanding of quantum geometric responses in a wide range of crystalline systems.
DOI: 10.1038/s41567-024-02678-8
Source: https://www.nature.com/articles/s41567-024-02678-8