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Low-frequency divergence and quantum geometry of the bulk photovoltaic effect in topological semimetals | | Junyeong Ahn
; Naoto Nagaosa
; | | Date: |
11 Jun 2020 | | 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, 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
$omega^{-2}$ and $omega^{-1}$ 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. Our work brings out new insights into the structure of
nonlinear optical responses as well as for the design of semimetal-based
terahertz photodetectors. | | Source: | arXiv, 2006.6709 | | Services: | Forum | Review | PDF | Favorites | |
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