Institute of Physics and Applied Physics, Yonsei University, Seoul 03722, Korea.
Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea.
Phys Rev Lett. 2018 Nov 2;121(18):186401. doi: 10.1103/PhysRevLett.121.186401.
We investigate the hidden Berry curvature in bulk 2H-WSe_{2} by utilizing the surface sensitivity of angle resolved photoemission (ARPES). The symmetry in the electronic structure of transition metal dichalcogenides is used to uniquely determine the local orbital angular momentum (OAM) contribution to the circular dichroism (CD) in ARPES. The extracted CD signals for the K and K^{'} valleys are almost identical, but their signs, which should be determined by the valley index, are opposite. In addition, the sign is found to be the same for the two spin-split bands, indicating that it is independent of spin state. These observed CD behaviors are what are expected from Berry curvature of a monolayer of WSe_{2}. In order to see if CD-ARPES is indeed representative of hidden Berry curvature within a layer, we use tight binding analysis as well as density functional calculation to calculate the Berry curvature and local OAM of a monolayer WSe_{2}. We find that measured CD-ARPES is approximately proportional to the calculated Berry curvature as well as local OAM, further supporting our interpretation.
我们通过利用角分辨光电子能谱（ARPES）的表面灵敏度来研究体 2H-WSe_{2}中的隐藏 Berry 曲率。过渡金属二卤化物的电子结构中的对称性被用来唯一确定 ARPES 中圆二色性（CD）的局域轨道角动量（OAM）贡献。对于 K 和 K^{'} 谷，提取的 CD 信号几乎相同，但它们的符号，应该由谷指数决定，是相反的。此外，两个自旋劈裂带的符号相同，表明它与自旋态无关。这些观察到的 CD 行为是单层 WSe_{2}的 Berry 曲率所预期的。为了确定 CD-ARPES 是否确实代表了层内的隐藏 Berry 曲率，我们使用紧束缚分析以及密度泛函计算来计算单层 WSe_{2}的 Berry 曲率和局域 OAM。我们发现，所测量的 CD-ARPES 与计算的 Berry 曲率以及局域 OAM 大致成正比，这进一步支持了我们的解释。
