Revealing the hidden Dirac gap in a topological antiferromagnet using Floquet-Bloch manipulation

TL;DR

This study demonstrates that Floquet-Bloch manipulation using circularly polarized light can control the Dirac surface-state mass gap in a topological antiferromagnet, revealing new ways to manipulate topological phases even with disorder.

Contribution

It provides the first experimental evidence of Floquet-Bloch control of Dirac mass gaps in a topological magnetic system with disorder, using time-resolved photoemission spectroscopy.

Findings

Opposite helicities of light induce different Dirac mass gaps.

Equilibrium Dirac cone remains massless despite manipulation.

Floquet-Bloch control is effective in disordered topological materials.

Abstract

Manipulating solids using the time-periodic drive of a laser pulse is a promising route to generate new phases of matter. Whether such `Floquet-Bloch' manipulation can be achieved in topological magnetic systems with disorder has so far been unclear. In this work, we realize Floquet-Bloch manipulation of the Dirac surface-state mass of the topological antiferromagnet (AFM) MnBi$_2$Te$_4$. Using time- and angle-resolved photoemission spectroscopy (tr-ARPES), we show that opposite helicities of mid-infrared circularly polarized light result in substantially different Dirac mass gaps in the AFM phase, despite the equilibrium Dirac cone being massless. We explain our findings in terms of a Dirac fermion with a random mass. Our results underscore Floquet-Bloch manipulation as a powerful tool for controlling topology even in the presence of disorder, and for uncovering properties of materials that may elude conventional probes.