Optical conductivity and orbital magnetization of Floquet vortex states

TL;DR

This paper investigates how light with orbital angular momentum induces orbital magnetization and affects optical conductivity in Floquet vortex states, proposing experimental detection methods for these states.

Contribution

It provides a theoretical analysis of orbital magnetization and optical conductivity in Floquet vortex states induced by structured light, highlighting measurable effects and detection schemes.

Findings

Orbital magnetization density increases linearly with OAM of light.

Magnetization from Floquet states is large and detectable via magnetometry.

Optical conductivity reveals signatures of vortex, edge, and bulk states.

Abstract

Motivated by recent experimental demonstrations of Floquet topological insulators, there have been several theoretical proposals for using structured light, either spatial or spectral, to create other properties such as flat band and vortex states. In particular, the generation of vortex states in a massive Dirac fermion insulator irradiated by light carrying nonzero orbital angular momentum (OAM) has been proposed [Kim et al. Phys. Rev. B 105, L081301(2022)]. Here, we evaluate the orbital magnetization and optical conductivity as physical observables for such a system. We show that the OAM of light induces nonzero orbital magnetization and current density. The orbital magnetization density increases linearly as a function of OAM degree. In certain regimes, we find that orbital magnetization density is independent of the system size, width, and Rabi frequency of light. It is shown that the orbital magnetization arising from our Floquet theory is large and can be probed by magnetometry measurements. Furthermore, we study the optical conductivity for various types of electron transitions between different states such as vortex, edge, and bulk that are present in the system. Based on conductance frequency peaks, a scheme for the detection of vortex states is proposed.