Photogalvanic currents from first-principles real-time density-matrix dynamics

TL;DR

This paper introduces a first-principles real-time density matrix formalism to accurately calculate photogalvanic currents in non-centrosymmetric materials, accounting for all quantum scatterings and connecting with quantum geometric properties.

Contribution

It develops a comprehensive first-principles framework for photogalvanic currents that includes all quantum scatterings and applies to transient and steady regimes, advancing beyond previous studies.

Findings

Phonon-mediated electron scatterings significantly affect the shift current in piezoelectrics.

A self-consistent theory of steady injection current incorporating phonon scattering is developed.

The formulation links photogalvanic effects with quantum geometric quantities like Berry curvature.

Abstract

The photogalvanic effect is the generation of a second-order direct current by illumination of a non-centrosymmetric material. In this work, we develop a first-principles real-time density matrix (FPDMD) formalism enabling the calculations of the photogalvanic current in all time regimes: transient and steady. Unlike past \textit{ab-initio} studies which focused only on the photo-excitation process, our first-principles theory framework encodes all quantum scatterings (intra/interband relaxation and electron-hole recombination) mediated by bosons (photons and phonons), and is thus predictive of photogalvanic currents in realistic materials. In particular, for the linear photogalvanic effect, we find electron scatterings mediated by phonons contribute significantly to the shift current for prototypical piezoelectrics like BaTiO$_3$. For the circular photogalvanic effect, we develop a self-consistent theory of a steady injection current that incorporates realistic scattering mediated by phonons. Our formulation developed for photogalvanic current elucidates its connection with fundamental quantum-geometric quantities such as the Berry curvature and the quantum metric. A phonon-based explanation is proposed for the bipolar transient photogalvanic current observed by the THz emission spectroscopy.