Floquet optical selection rules in black phosphorus

TL;DR

This paper develops a symmetry-based framework using Floquet theory and TDDFT to understand and predict the optical selection rules and spectral features in monolayer black phosphorus under ultrafast laser excitation.

Contribution

It introduces momentum-resolved Floquet optical selection rules for black phosphorus and demonstrates their effectiveness in explaining photoemission spectra through a combination of group theory and TDDFT.

Findings

Floquet optical selection rules explain photoemission spectral distributions.

Spectral weights at specific momenta are identified for Floquet states.

The framework predicts new spectral features under various pump-probe setups.

Abstract

Optical selection rules endorsed by symmetry are crucial for understanding the optical properties of quantum materials and the associated ultrafast spectral phenomena. Here, we introduce momentum-resolved Floquet optical selection rules using group theory to elucidate the pump-probe photoemission spectral distributions of monolayer black phosphorus (BP), which are governed by the symmetries of both the material and the lasers. Using time-dependent density functional theory (TDDFT), we further investigate the dynamical evolution of Floquet(-Volkov) states in the photoemission spectra of monolayer BP, revealing their spectral weights at specific momenta for each sideband. These observations are comprehensively explained by the proposed Floquet optical selection rules. Our framework not only clarifies experimental photoemission spectra but also uncovers unexplored characteristics under different pump-probe configurations. Our results are expected to deepen the understanding of light-induced ultrafast spectra in BP and can be extended to other Floquet systems.