Circular dichroism in high-order harmonic generation: Heralding topological phases and transitions in Chern insulators

TL;DR

This paper demonstrates that high-harmonic generation with circularly polarized lasers can detect topological phase transitions in Chern insulators by revealing distinct circular dichroism signatures.

Contribution

It introduces a novel method using high-harmonic generation to identify topological phases and transitions in topological materials like the Haldane model.

Findings

High-harmonic emission shows shifts in emissivity and cutoff at phase transitions.

Circular dichroism in HHG signals changes distinctly at topological boundaries.

The method offers a new ultrafast spectroscopy tool for topological materials.

Abstract

Topological materials are of interest to both fundamental science and advanced technologies, because topological states are robust with respect to perturbations and dissipation. Experimental detection of topological invariants is thus in great demand, but it remains extremely challenging. Ultrafast laser-matter interactions, and in particular high-harmonic generation (HHG), meanwhile, were proposed several years ago as tools to explore the structural and dynamical properties of various matter targets. Here we show that the high-harmonic emission signal produced by a circularly-polarized laser contains signatures of the topological phase transition in the paradigmatic Haldane model. In addition to clear shifts of the overall emissivity and harmonic cutoff, the high-harmonic emission shows a unique circular dichroism, which exhibits clear changes in behavior at the topological phase boundary. Our findings pave the way to understand fundamental questions about the ultrafast electron-hole pair dynamics in topological materials via non-linear high-harmonic generation spectroscopy.