Nonlinear response theory for orbital photocurrent in semiconductors

TL;DR

This paper develops a comprehensive theory for calculating nonlinear orbital and spin photocurrents in semiconductors, analyzing their behavior near topological phase transitions and their dependence on relaxation times.

Contribution

It introduces a general framework for nonlinear spin and orbital current calculations applicable to complex material models, with specific analysis of topological phase transitions.

Findings

Orbital responses exhibit distinct evolution at topological phase transitions.

Relaxation time influences orbital conductivity differently from photocurrent.

The theory enables quantitative predictions for real material responses.

Abstract

Recent theoretical studies on the nonlinear response of spin and orbital degrees of freedom have discovered spin and orbital analogs of the photocurrent, with potential for characterizing topological materials and for applications. In this paper, we develop a general theory for calculating spin and orbital currents in semiconductors and study the properties of optical responses in the Bernevig-Hughes-Zhang and Luttinger models, where nonlinear orbital responses and a topological phase transition occur. We study the evolution of optical responses at the topological phase transition and how they manifest. In addition, we find that the relaxation time dependence of the orbital conductivity is somewhat distinct from that of the photocurrent. The theory is straightforwardly applicable to complex models of real materials, allowing quantitative predictions of the nonlinear responses of orbital and spin.