Observation of Floquet-induced gap in graphene

TL;DR

This study experimentally demonstrates Floquet band engineering in graphene by observing a light-induced hybridization gap using time- and angle-resolved photoemission spectroscopy, revealing tunable, anisotropic Floquet states.

Contribution

First direct observation of a Floquet-induced hybridization gap in graphene, confirming theoretical predictions and advancing non-equilibrium quantum phase control.

Findings

Gap opening at Floquet band crossings observed

Floquet sidebands detected alongside the gap

Gap tunable by light polarization and exhibits momentum anisotropy

Abstract

Floquet engineering provides a powerful pathway for creating non-equilibrium phases of matter with tailored electronic structures and properties through time-periodic driving. As the original theoretical prototype, graphene established the framework in which the Floquet topological insulator with light-induced anomalous Hall effect was proposed. However, the defining spectroscopic signature of Floquet engineering in graphene--light-induced hybridization (avoided-crossing) gap at Floquet band crossings, has remained experimentally elusive. Here, we report direct observation of Floquet-induced hybridization gap in monolayer graphene under resonant driving by a strong light field. Time- and angle-resolved photoemission spectroscopy reveals gap opening at Floquet band crossings, accompanied by coherent Floquet sidebands. The gap exhibits pronounced momentum anisotropy, featuring two Dirac nodes protected by the spatiotemporal symmetry and tunable by light polarization. These results provide long-sought experimental demonstration of Floquet band engineering in graphene, opening up opportunities for light-field engineered quantum phases in graphene and related materials.