On the survival of Floquet-Bloch states in the presence of scattering

TL;DR

This study investigates how scattering affects the formation and stability of Floquet-Bloch states in solids under light, revealing that high scattering rates hinder their survival unless driven strongly at high fields.

Contribution

It combines experimental and theoretical approaches to elucidate the conditions under which Floquet-Bloch states can persist despite scattering effects.

Findings

Floquet-Bloch states are destroyed by scattering when electrons cannot follow the driving field.

High field intensities can restore Floquet-Bloch states despite scattering.

Long scattering times and strong driving fields are crucial for realizing Floquet phenomena.

Abstract

Floquet theory has spawned many exciting possibilities for electronic structure control with light with enormous potential for future applications. The experimental realization in solids, however, largely remains pending. In particular, the influence of scattering on the formation of Floquet-Bloch states remains poorly understood. Here we combine time- and angle-resolved photoemission spectroscopy with time-dependent density functional theory and a two-level model with relaxation to investigate the survival of Floquet-Bloch states in the presence of scattering. We find that Floquet-Bloch states will be destroyed if scattering -- activated by electronic excitations -- prevents the Bloch electrons from following the driving field coherently. The two-level model also shows that Floquet-Bloch states reappear at high field intensities where energy exchange with the driving field dominates over energy dissipation to the bath. Our results clearly indicate the importance of long scattering times combined with strong driving fields for the successful realization of various Floquet phenomena.