Dynamical polarizability of graphene irradiated by circularly polarized ac electric fields

TL;DR

This paper investigates how a circularly polarized terahertz electric field affects the dynamical polarizability and excitation properties of graphene, revealing new collective behaviors and stability conditions.

Contribution

It provides a general expression for graphene's dynamical polarizability under ac fields and develops a semi-analytical theory for weak fields, highlighting qualitative changes in excitations.

Findings

External ac field induces collective excitations in undoped graphene.

Doped graphene's excitation properties are strongly modified by the ac field.

Field intensity controls the stability of excitations.

Abstract

We examine the low-energy physics of graphene in the presence of a circularly polarized electric field in the terahertz regime. Specifically, we derive a general expression for the dynamical polarizability of graphene irradiated by an ac electric field. Several approximations are developed that allow one to develop a semianalytical theory for the weak field regime. The ac field changes qualitatively the single and many electron excitations of graphene: undoped samples may exhibit collective excitations (in contrast to the equilibrium situation), and the properties of the excitations in doped graphene are strongly influenced by the ac field. We also show that the intensity of the external field is the critical control parameter for the stability of these excitations.