Ab initio study of quantized circular photogalvanic effect in chiral multifold semimetals

Congcong Le,Yan Sun,Yang Zhang,Claudia Felser

doi:10.1103/physrevb.102.121111

Abstract

So far, the circular photogalvanic effect (CPGE) is the only possible quantized signal in Weyl semimetals. With inversion and mirror symmetries broken, Weyl and multifold fermions in band structures with opposite chiralities can stay at different energies and generate a net topological charge. Such a kind of net topological charge can present as a quantized signal in the circular polarized light-induced injection current. According to current theoretical understanding, RhSi and its counterparts are believed to be the most promising candidates for the experimental observation of the quantized CPGE. However, a real quantized signal has yet to be experimentally observed. Since previous theoretical studies for the quantized CPGE were based on an effective model but not realistic band structures, it should lose some crucial details that influence the quantized signal. The current status motivates us to perform a realistic ab initio study for the CPGE. Our result shows that RhSi and PtAl in chiral multifold semimetals are alternative materials for obtaining the quantized CPGE which is very easy to be interfered with by trivial band-related optic transitions, and a fine tuning of the chemical potential by doping is essential for the observation of the quantized CPGE. We perform an ab initio analysis for the quantized CPGE based on a realistic electronic band structure and provide an effective way to solve the current problem for the given materials.

Highlights

Band crossings with a nontrivial topological invariant, including Weyl, Dirac, and unconventional fermions, have been attracting enormous attention in condensed matter [1,2,3]
It has been pointed out [31,32,33] that a single multifold degenerate point with a nontrivial invariant can lead to a quantized circular photogalvanic effect (CPGE) trace, which can directly measure the topological charge of degenerate points
The circular photogalvanic effect (CPGE) of topological semimetals with chiral multifold fermions was calculated based on realistic ab initio band structures

Summary

INTRODUCTION

Band crossings with a nontrivial topological invariant, including Weyl, Dirac, and unconventional fermions, have been attracting enormous attention in condensed matter [1,2,3]. Unconventional fermions, which contain three-, four-, six-, and eightfold degenerate points, have been exhaustively classified by space group symmetries in solid-state systems with spin-orbit coupling and time-reversal symmetry These multifold degenerate points with nontrivial topological numbers lead to a series of exotic effects such as surface Fermi arcs [4,5], the chiral anomaly [21,22], large anomalous Hall and spin Hall effects [23,24,25], and circular photogalvanic effects [26,27,28,29,30,31,32]. Nonmagnetic chiral topological semimetal materials with a chiral space group, only including time-reversal and rotational symmetries, have different energies for degenerate points with opposite charge and can realize a true quantized CPGE trace due to Pauli blocking.

DIFFERENCE BETWEEN EFFECTIVE MODEL AND REAL MATERIALS

SYMMETRY ANALYSIS OF CPGE TENSOR

CONCLUSION