Microscopic electron dynamics in nonlinear optical response of solids

TL;DR

This paper explores the microscopic electron dynamics underlying nonlinear optical responses in solids, revealing complex charge distributions and developing a method to reconstruct these distributions using advanced x-ray techniques.

Contribution

It introduces a novel framework combining Floquet theory and x-ray wave mixing to analyze and visualize microscopic charge dynamics in crystalline solids.

Findings

Microscopic charge distributions can be nonzero even when macroscopic responses are forbidden.

Charge redistribution exhibits complex spatial structures governed by crystal symmetries.

A method for reconstructing microscopic charge distributions via subcycle-resolved x-ray wave mixing is developed.

Abstract

We investigate the microscopic properties of the nonlinear optical response of crystalline solids within Floquet theory, and demonstrate that optically-induced microscopic charge distributions display complex spatial structure and nontrivial properties. Their spatial symmetry and temporal behavior are governed by crystal symmetries. We find that even when a macroscopic optical response of a crystal is forbidden, the microscopic optical response can, in fact, be nonzero. In such a case, the optically-induced charge redistribution can be considerable, even though the corresponding Fourier component of the time-dependent dipole moment per unit cell vanishes. We develop a method that makes it possible to completely reconstruct the microscopic optically-induced charge distributions by means of subcycle-resolved x-ray-optical wave mixing. We also show how, within this framework, the direction of the instantaneous microscopic optically-induced electron current flow can be revealed.