Hallmarks of spin textures for high-harmonic generation in two-dimensional materials

TL;DR

This paper explores how spin textures and Berry curvature influence high-harmonic generation in 2D materials, revealing that symmetry breaking is crucial for even-order harmonics and that HHG can probe electronic phase transitions.

Contribution

It uncovers the role of spin texture symmetry breaking and Berry curvature in enabling even-order high-harmonics in 2D materials, offering new insights into nonlinear optical phenomena.

Findings

Finite even-order harmonics require broken twofold rotational symmetry.

HHG is sensitive to dynamical rotational-symmetry breaking.

HHG can probe electronic phase transitions with broken symmetry.

Abstract

Spin-orbit coupling and quantum geometry are fundamental aspects in modern condensed matter physics, with their primary manifestations in momentum space being spin textures and Berry curvature. In this work, we investigate their interplay with high-harmonic generation (HHG) in two-dimensional non-centrosymmetric materials, with an emphasis on even-order harmonics. Our analysis reveals that the emergence of finite even-order harmonics necessarily requires a broken twofold rotational symmetry in the spin texture, as well as a non-trivial Berry curvature in systems with time-reversal invariance. This symmetry breaking can arise across various degrees of freedom and impact both spin textures and optical response via spin-orbit interactions. We also show that HHG is particularly sensitive to dynamical rotational-symmetry breaking, as even high-order components can be modulated by a time-dependent symmetry breaking. These findings underscore the potential of HHG as a tool for exploring electronic phases with broken rotational symmetry, as well as the associated phase transitions in two-dimensional materials, and provide novel perspectives for designing symmetry-dependent nonlinear optical phenomena.