Origin of nonlinear photocurrents in chiral multifold semimetal CoSi unveiled by terahertz emission spectroscopy

TL;DR

This study uses terahertz emission spectroscopy to analyze nonlinear photocurrents in chiral multifold CoSi, revealing large and complex photoconductivity contributions linked to topological features, with implications for photovoltaic applications.

Contribution

It provides a comprehensive spectroscopic analysis of nonlinear photocurrents in CoSi, identifying large injection and shift conductivities and unveiling complex current components and effects.

Findings

Large linear shift conductivity of 17 μA/V²

Giant injection conductivity of 167 μA/V² near multifold nodes

Detection of weak nonlocal photon drag effect

Abstract

Spectroscopic identification of distinct nonlinear photocurrents unveils quantum geometric properties of electron wavefunctions and the momentum-space topological structures. This is especially interesting, but still puzzling, for chiral topological semimetals with possibilities of hosting giant quantized circular photogalvanic effect. Here we report a comprehensive terahertz (THz) emission spectroscopic analysis of nonlinear photoconductivity of chiral multifold CoSi at 0.26 ~ 1 eV. We find a large linear shift conductivity (17 {\mu}A/V2), and confirm a giant injection conductivity (167 {\mu}A/V2) as a consequence of strongly interfered non-quantized contributions from the vicinity of multifold nodes with opposite chiralities. The bulk injection current excited by the pump field with a complex wavevector is shown to carry both longitudinal and transverse components. Symmetry analyses further unveil weak nonlocal photon drag effect in addition to the photogalvanic effect. This work not only highlights chiral transition metal monosilicides for mid-infrared photovoltaic applications via various nonlinear optical channels, but also consolidates the THz spectroscopy for quantitative photovoltaic research.