Floquet topological state induced by light-driven band inversion in SnTe

TL;DR

This paper reports the first experimental observation of a light-induced Floquet topological state in SnTe, achieved through femtosecond pulses that cause band inversion, enabling optically controlled topological properties.

Contribution

It demonstrates the creation of a non-equilibrium topological state in SnTe via Floquet engineering using ultrafast light pulses, a novel experimental realization.

Findings

Observation of a transient Floquet topological state in SnTe

Band dispersion renormalization indicating Floquet state formation

Evidence of light-induced band inversion in a semiconductor

Abstract

High intensity coherent light can dress matter, realizing new hybrid phases that are not accessible in equilibrium. This effect results from the coherent interaction between Bloch states inside the solid and the periodic field of impinging photons which produces hybrid light-matter states called Floquet-Bloch states that can alter properties of the solid. Optically inducing a topological state in a semiconductor using so-called Floquet engineering is an exciting prospect. However, it has not been realized, despite its theoretical prediction more than 10 years ago. Here we show that an ultrashort-lived topological state that is absent at equilibrium in the ground state of SnTe can be created with femtosecond light pulses. This occurs when the photoexcitation is similar in energy with the band gap of this polar semiconductor. We observe a concomitant renormalization of the band dispersions that reveals the generation of Floquet states connecting to the topological state. We therefore provide the first direct experimental observation of a Floquet topological state and propose that it is driven by a light-induced band inversion in SnTe. Our discovery opens the way for controlling optically on-demand the topological properties of semiconductors.