Direct observation of a photoinduced topological phase transition in Bi-doped (Pb,Sn)Se

TL;DR

This study demonstrates the direct observation of a photoinduced topological phase transition in Bi-doped (Pb,Sn)Se films, showing that ultrafast laser pulses can switch the material from topological to trivial insulator states by opening a surface state gap.

Contribution

First direct visualization of a topological phase transition induced by ultrafast optical excitation in a topological insulator material.

Findings

Ultrafast laser excitation opens a gap in the topological surface state up to 0.1 eV.

Uniaxial strain from optical pulses drives the topological phase transition.

Optical control can manipulate topological properties on ultrafast timescales.

Abstract

Ultrafast photoexcitation offers a novel approach to manipulating quantum materials. One of the long-standing goals in this field is to achieve optical control over topological properties. However, the impact on their electronic structures, which host gapless surface states, has yet to be directly observed. Here, using time- and angle-resolved photoemission spectroscopy, we visualize the photo-induced evolution of the band structure in Biy(Pb1-xSnx)1-ySe(111) films from topological to trivial insulators. Following near-infrared ultrafast laser excitation, we observe that the topological surface state opens a substantial gap of up to 0.1 eV. Considering the topological phase diagram associated with lattice distortion and atomic displacement, we show that a uniaxial strain generated by the ultrafast optical pulse is sufficiently effective and strong for the observed topological phase transition. Our study highlights the potential of optical tuning of materials through laser excitation to control topological properties on ultrafast timescales.