Transverse current current response of graphene at finite temperature, plasmons and absorption

TL;DR

This paper investigates the finite-temperature transverse current response of graphene, exploring transverse plasmons, their confinement, and electromagnetic absorption, revealing conditions for maximal confinement and the absence of transverse plasmons at zero doping.

Contribution

It provides a detailed analysis of transverse plasmons in graphene at finite temperature, including their dependence on dielectric environment and cavity effects, which was not extensively studied before.

Findings

Maximal confinement occurs for dielectric index n≈40

Transverse plasmons are absent at zero doping and finite temperature

Absorption reaches 50% for s-polarized light at near-grazing incidence

Abstract

We calculate the linear transverse current current response function for graphene at finite temperature and chemical potential. Within the Random Phase Approximation, we then discuss general aspects of transverse plasmons beyond the local response such as their dependence on temperature and on the surrounding dielectric media. We find, e.g., maximal confinement of this mode for a homogeneous dielectric media with refractive index $n\simeq 40$. Confinement can further be enhanced by placing the graphene sheet inside an optical cavity, but there exists a critical width below which no transverse mode can be sustained. For zero doping and finite temperature, there are no well-defined transverse plasmonic excitations in contrast to the longitudinal channel. We also discuss the absorption of electromagnetic radiation in single and double-layer systems for $s$ and $p$ polarizations and point out that the theoretical limit of 50% is reached for $s$-polarized light with incident angle of $\theta\approx89^o$.