Photocurrents induced by k-linear terms in semiconductors and semimetals

TL;DR

This paper develops a six-band model to analyze the optical and photocurrent responses of chiral multifold semimetals, highlighting the effects of Rashba coupling and topology on their optoelectronic properties.

Contribution

It introduces an effective Hamiltonian incorporating Rashba and spin-orbit effects, providing analytical insights into the optical absorption and photocurrent phenomena in multifold semimetals.

Findings

Linear-in-frequency interband absorption at low energies

Resonant feature near spin-orbit splitting energy

Quantized low-frequency photocurrent response with universal charge value

Abstract

We develop a six-band $\mathbf{k} \cdot \mathbf{p}$ model to describe the electronic structure and optical response of chiral multifold semimetals, such as RhSi. By means of invariants method we construct the effective Hamiltonian describing the states near the $\Gamma$-point of the Brillouin zone where the spin-orbit coupling and $\mathbf{k}$-linear Rashba terms, which are crucial for circular photogalvanic effect, are taken into account. The model is parameterized using tight-binding calculations. We compute the interband absorption spectrum, showing a linear-in-frequency dependence at low energies and a resonant feature near the spin-orbit splitting energy. Furthermore, we calculate the circular photogalvanic effect. In agreement with previous works the current generation rate at low frequencies exhibits a quantized low-frequency response, governed by the universal value $|\mathcal{C}| = 4$ for the effective topological charge. Our results provide an analytical framework for understanding the role of Rashba coupling and topology in the optoelectronic properties of multifold chiral semimetals.