Probing Topological Floquet States in WSe$_2$ using Circular Dichroism in Time- and Angle-Resolved Photoemission Spectroscopy

TL;DR

This study demonstrates how circular dichroism in photoelectron angular distributions can reveal Floquet topological states in WSe$_2$, overcoming challenges like scattering and LAPE interference, with predictions applicable to current experimental setups.

Contribution

It introduces a method to identify Floquet topological states via CDAD in WSe$_2$, combining ab initio modeling with photoemission matrix elements to distinguish Floquet features.

Findings

Floquet topological states produce characteristic CDAD signatures.

Predicted features are robust against scattering effects.

Method applicable to current experimental conditions.

Abstract

Observing signatures of light-induced Floquet topological states in materials has been shown to be very challenging. Angle-resolved photoemission spectroscopy (ARPES) is well suited for the investigation of Floquet physics, as it allows to directly probe the dressed electronic states of driven solids. Depending on the system, scattering and decoherence can play an important role, hampering the emergence of Floquet states. Another challenge is to disentangle Floquet side bands from laser-assisted photoemission (LAPE), since both lead to similar signatures in ARPES spectra. Here, we investigate the emergence of Floquet state in the transition metal dichalcogenide $2H$-WSe$_2$, one of the most promising systems for observing Floquet physics. We discuss how the Floquet topological state manifests in characteristic features in the circular dichroism in photoelectron angular distributions (CDAD) that is determined by the transient band structure modifications and the associated texture of the orbital angular momentum. Combining highly accurate modeling of the photoemission matrix elements with an \emph{ab initio} description of the light-matter interaction, we investigate regimes which can be realized in current state-of-the-art experimental setups. The predicted features are robust against scattering effects and are expected to be observed in forthcoming experiments.