All-optical probe of three-dimensional topological insulators based on high-harmonic generation by circularly-polarized laser fields

TL;DR

This paper demonstrates a novel nonlinear optical response in topological insulators using high-harmonic generation with circularly polarized lasers, revealing insights into their band topology and potential for ultrafast applications.

Contribution

It introduces an all-optical, contact-free method to probe topological insulators via high-harmonic generation, highlighting the role of circular polarization in enhancing signals.

Findings

Harmonic generation efficiency peaks at circular polarization.

The enhancement encodes the topological band structure.

Provides a new platform for ultrafast topological studies.

Abstract

We report the observation of a novel nonlinear optical response from the prototypical three-dimensional topological insulator Bi$_2$Se$_3$ through the process of high-order harmonic generation. We find that the generation efficiency increases as the laser polarization is changed from linear to elliptical, and it becomes maximum for circular polarization. With the aid of a microscopic theory and a detailed analysis of the measured spectra, we reveal that such anomalous enhancement encodes the characteristic topology of the band structure that originates from the interplay of strong spin-orbit coupling and time-reversal symmetry protection. Our study reveals a new platform for chiral strong-field physics and presents a novel, contact-free, all-optical approach for the spectroscopy of topological insulators. The implications are in ultrafast probing of topological phase transitions, light-field driven dissipationless electronics, and quantum computation.