Occupation Dynamics of Floquet-Volkov States and Spectral Sum Rule

TL;DR

This study uses time- and angle-resolved photoemission spectroscopy to investigate the occupation and spectral weight conservation of Floquet-Volkov states in black phosphorus and MoSe2 under periodic light fields, revealing insights into their population dynamics.

Contribution

It demonstrates that while individual Floquet sidebands' occupation varies with the driving field, the total spectral weight remains conserved, providing new understanding of Floquet state dynamics.

Findings

Occupation of Floquet-Volkov states depends on the driving field.

Total spectral weight of Floquet sidebands is conserved below the gap.

Insights into Floquet population dynamics for transient material property control.

Abstract

Time-periodic light fields can dress electronic states in quantum materials, forming Floquet states whose dynamic occupation determines transient material properties. Here by using time- and angle-resolved photoemission spectroscopy (TrARPES), we reveal the transient occupation of Floquet-Volkov states in two semiconductors, black phosphorus and MoSe$_2$. While the occupation of the light-induced sidebands, directly reflected by TrARPES spectral weight, strongly depends on the driving field, we find that the total spectral weight obtained by summing up all sidebands is conserved upon below-gap driving. Our work provides critical insights into the Floquet population dynamics, which are essential for light-field tailoring of transient material properties.