Nonlocal Optical Response in Topological Phase Transitions in the Graphene Family

TL;DR

This paper explores how the optical and plasmonic responses of graphene family materials change during topological phase transitions, highlighting the importance of nonlocal effects in their electromagnetic behavior.

Contribution

It provides a comprehensive calculation of the optical conductivity tensor considering nonlocal effects across the full phase diagram of these materials.

Findings

Nonlocal optical response influences plasmon dispersion spectra.

Conductivity expressions are applicable to the entire graphene family.

Electromagnetic response varies significantly across topological phases.

Abstract

We investigate the electromagnetic response of staggered two-dimensional materials of the graphene family, including silicene, germanene, and stanene, as they are driven through various topological phase transitions using external fields. Utilizing Kubo formalism, we compute their optical conductivity tensor taking into account the frequency and wave vector of the electromagnetic excitations, and study its behavior over the full electronic phase diagram of the materials. We also consider the plasmon excitations in the graphene family and find that nonlocality in the optical response can affect the plasmon dispersion spectra of the various phases. The expressions for the conductivity components are valid for the entire graphene family and can be readily used by others.