论文标题
拓扑半学的散装光伏效应的低频差异和量子几何形状
Low-frequency divergence and quantum geometry of the bulk photovoltaic effect in topological semimetals
论文作者
论文摘要
我们研究了拓扑半学中大量光伏效应的低频性能。大量光伏效应是一种非线性光学效应，它在均匀的辐射下产生直流光电流，这是非中心对称性的。这是基于拓扑半学的Terahertz光反定程的有希望的机制。在这里，我们系统地研究了点节点半学中二阶光导率的低频行为。通过对称和功率计数分析，我们表明带有倾斜锥的狄拉克和Weyl点显示了领先的低频差异。特别是，我们在圆形极化的光下发现了狄拉克和Weyl点的电导率的新不同行为，其中电导率缩放为$ω^{ - 2} $和$ω^{ - 1} $，分别在两个和三个维度的间隙关闭点附近。我们通过揭示二阶光学电导率张量的完整量子几何含义，对低频大量光伏效应提供进一步的观点。大量光伏效应具有两个起源，它们是电子位置的过渡和光激发期间电子速度的过渡，所得的光电流分别称为移位电流和注入电流。基于对两种波段模型的分析，我们表明注射电流由量子度量标准和浆果曲率控制，而移位电流则由半距离隔离点附近的christoffel符号控制。最后，为了进一步演示我们的理论，超出了简单的两波段模型，我们对磁性狄拉克半学MNGEO $ _3 $和WEYL SEMIMITAL PRGEAL进行了第一原理计算。我们的工作为非线性光学响应的结构以及基于半学的Terahertz光电探测器的设计提供了新的见解。
We study the low-frequency properties of the bulk photovoltaic effect in topological semimetals. The bulk photovoltaic effect is a nonlinear optical effect that generates DC photocurrents under uniform irradiation, allowed by noncentrosymmetry. It is a promising mechanism for a terahertz photodetection based on topological semimetals. Here, we systematically investigate the low-frequency behavior of the second-order optical conductivity in point-node semimetals. Through symmetry and power-counting analysis, we show that Dirac and Weyl points with tilted cones show the leading low-frequency divergence. In particular, we find new divergent behaviors of the conductivity of Dirac and Weyl points under circularly polarized light, where the conductivity scales as $ω^{-2}$ and $ω^{-1}$ near the gap-closing point in two and three dimensions, respectively. We provide a further perspective on the low-frequency bulk photovoltaic effect by revealing the complete quantum geometric meaning of the second-order optical conductivity tensor. The bulk photovoltaic effect has two origins, which are the transition of electron position and the transition of electron velocity during the optical excitation, and the resulting photocurrents are respectively called the shift current and the injection current. Based on an analysis of two-band models, we show that the injection current is controlled by the quantum metric and Berry curvature, whereas the shift current is governed by the Christoffel symbols near the gap-closing points in semimetals. Finally, for further demonstrations of our theory beyond simple two-band models, we perform first-principles calculations on magnetic Dirac semimetal MnGeO$_3$and Weyl semimetal PrGeAl. Our work brings out new insights into the structure of nonlinear optical responses as well as for the design of semimetal-based terahertz photodetectors.
