https://scholars.lib.ntu.edu.tw/handle/123456789/573452
Title: | Low-Frequency Divergence and Quantum Geometry of the Bulk Photovoltaic Effect in Topological Semimetals | Authors: | Junyeong Ahn Guang-Yu Guo Naoto Nagaosa GUANG-YU GUO |
Keywords: | Aluminum compounds; Calculations; Geometry; Germanium compounds; Magnetic anisotropy; Magnetization; Manganese compounds; Nonlinear optics; Optical conductivity; Photocurrents; Photodetectors; Praseodymium compounds; Tensors; Topology; Circularly polarized light; Conductivity tensors; First-principles calculation; Geometric quantities; Low frequency behavior; Magnetization orientation; Nonlinear optical effects; Nonlinear optical response; Photovoltaic effects | Issue Date: | 2020 | Journal Volume: | 10 | Journal Issue: | 4 | Source: | Physical Review X | Abstract: | 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, which is 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 the shift and injection photocurrent conductivities as well as geometric quantities of antiferromagnetic MnGeO3 and ferromagnetic PrGeAl, respectively, as representatives of real magnetic Dirac and Weyl semimetals. Our calculations reveal gigantic peaks in many nonvanishing elements of photoconductivity tensors below a photon energy of about 0.2 eV in both MnGeO3 and PrGeAl. In particular, we show the ω-1 enhancement of the shift conductivity tensors due to the divergent behavior of the geometric quantities near the Dirac and Weyl points as well as slightly gapped topological nodes. Moreover, the low-frequency bulk photovoltaic effect is tunable by carrier doping and magnetization orientation rotation. Our work brings new insights into the structure of nonlinear optical responses as well as the design of semimetal-based terahertz photodetectors. ? 2020 authors. Published by the American Physical Society. |
URI: | https://www.scopus.com/inward/record.uri?eid=2-s2.0-85097586335&doi=10.1103%2fPhysRevX.10.041041&partnerID=40&md5=dbe81af7d65a653657fe7f95f545acf9 https://scholars.lib.ntu.edu.tw/handle/123456789/573452 |
ISSN: | 21603308 | DOI: | 10.1103/PhysRevX.10.041041 | SDG/Keyword: | Aluminum compounds; Calculations; Geometry; Germanium compounds; Magnetic anisotropy; Magnetization; Manganese compounds; Nonlinear optics; Optical conductivity; Photocurrents; Photodetectors; Praseodymium compounds; Tensors; Topology; Circularly polarized light; Conductivity tensors; First-principles calculation; Geometric quantities; Low frequency behavior; Magnetization orientation; Nonlinear optical effects; Nonlinear optical response; Photovoltaic effects |
Appears in Collections: | 物理學系 |
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