Optical conductivity of the topologically-nontrivial MXenes, Mo$_2$HfC$_2$O$_2$ and W$_2$HfC$_2$O$_2$: first-principles calculation and effective model analysis

TL;DR

This paper investigates the optical conductivity of topologically nontrivial MXenes using first-principles calculations and effective models, revealing characteristic spectral features and their microscopic origins related to parity inversion.

Contribution

It introduces an effective model based on crystal symmetries to explain optical features in topologically nontrivial MXenes, linking them to electronic structure properties.

Findings

Characteristic optical conductivity features depend on photon energy and polarization.

Features are linked to parity inversion in electronic bands.

Effective model explains microscopic origins of spectral features.

Abstract

The optical conductivity and the relevant electronic excitation processes are investigated in topologically-nontrivial MXenes, Mo$_2$HfC$_2$O$_2$ and W$_2$HfC$_2$O$_2$, utilizing first-principles calculation and effective model analysis. The numerical calculation based on the first-principles band structure reveals the presence of several characteristic features in the spectrum of optical conductivity as a function of photon energy. The drastic dependence on the photon polarization angle is also presented in terms of apparent features. In this paper, an effective model is also generated referring to the crystal symmetries and applied to reveal the microscopic origin of the characteristics. Then, it is shown that some features are strongly related to parity inversion between the conduction and valence bands, the key signature in electronic structures of topologically nontrivial insulators.