Pseudospin-selective Floquet band engineering in black phosphorus

TL;DR

This study demonstrates pseudospin-selective Floquet band engineering in black phosphorus through experimental observation of band renormalization and dynamical gap opening using time- and angle-resolved photoemission spectroscopy, highlighting polarization-dependent effects.

Contribution

First experimental evidence of momentum-resolved Floquet band engineering in a semiconductor, revealing pseudospin selectivity influenced by lattice symmetry.

Findings

Observation of strong band renormalization near band edges

Detection of light-induced dynamical gap opening at resonance

Polarization-dependent Floquet effects favoring armchair direction

Abstract

Time-periodic light field has emerged as a control knob for manipulating quantum states in solid-state materials, cold atoms and photonic systems via hybridization with photon-dressed Floquet states in the strong coupling limit, dubbed as Floquet engineering. Such interaction leads to tailored properties of quantum materials, for example, modifications of the topological properties of Dirac materials and modulation of the optical response. Despite extensive research interests over the past decade, there is no experimental evidence of momentum-resolved Floquet band engineering of semiconductors, which is a crucial step to extend Floquet engineering to a wide range of solid-state materials. Here, based on time- and angle-resolved photoemission spectroscopy measurements, we report experimental signatures of Floquet band engineering in a model semiconductor - black phosphorus. Upon near-resonance pumping at photon energy of 340 to 440 meV, a strong band renormalization is observed near the band edges. In particular, light-induced dynamical gap opening is resolved at the resonance points, which emerges simultaneously with the Floquet sidebands. Moreover, the band renormalization shows a strong selection rule favoring pump polarization along the armchair direction, suggesting pseudospin selectivity for the Floquet band engineering as enforced by the lattice symmetry. Our work demonstrates pseudospin-selective Floquet band engineering in black phosphorus, and provides important guiding principles for Floquet engineering of semiconductors.