Polarization-dependent excitons and plasmon activity in nodal-line semimetal ZrSiS

TL;DR

This study investigates the optical properties of ZrSiS, revealing polarization-dependent excitonic effects and confirming theoretical predictions with experimental data, while dismissing low-energy plasma oscillations due to damping effects.

Contribution

It provides a detailed theoretical analysis of excitonic activity and polarization effects in ZrSiS, highlighting the role of dark and bright excitons and their dependence on electric field polarization.

Findings

Dark excitons dominate over bright excitons in ZrSiS.

Exciton energies and intensities depend strongly on polarization.

No activation of low-energy plasma oscillations due to damping.

Abstract

The optical properties of bulk ZrSiS nodal-line semimetal are theoretically studied within a many-body formalism. The G0W0 bands are similar to those calculated within the density functional theory, except near the {\Gamma} point; in particular, no significant differences are found around the Fermi energy. On the other hand, the solution of the Bethe-Salpeter equation reveals a significant excitonic activity, mostly as dark excitons which appear in a wide energy range. Bright excitons, on the contrary, are less numerous, but their location and intensity depend greatly on the polarization of the incident electric field, as the absorption coefficient itself does. The binding energy of these excitons correlate well with their spatial distribution functions. In any case, a good agreement with available experimental data for absorption-reflection is achieved. Finally, the possible activation of plasma oscillations at low energies is discarded, because these are damped by producing electron-hole pairs, more importantly for q along the {\Gamma}-M path.