Excitonic Instability and Pseudogap Formation in Nodal Line Semimetal ZrSiS

TL;DR

This study combines first-principles and model approaches to reveal excitonic instability and pseudogap formation in ZrSiS, explaining its unusual electronic properties and mass enhancement observed experimentally.

Contribution

It introduces a two-dimensional lattice model with parameters derived from first-principles calculations to describe electron correlations in ZrSiS, highlighting excitonic instability.

Findings

ZrSiS exhibits excitonic instability at low temperatures.

A pseudogap forms in the electronic spectrum due to electron-hole pairing.

The model explains the mass enhancement observed experimentally.

Abstract

Electron correlation effects are studied in ZrSiS using a combination of first-principles and model approaches. We show that basic electronic properties of ZrSiS can be described within a two-dimensional lattice model of two nested square lattices. High degree of electron-hole symmetry characteristic for ZrSiS is one of the key features of this model. Having determined model parameters from first-principles calculations, we then explicitly take electron-electron interactions into account and show that at moderately low temperatures ZrSiS exhibits excitonic instability, leading to the formation of a pseudogap in the electronic spectrum. The results can be understood in terms of Coulomb-interaction-assisted pairing of electrons and holes reminiscent to that of an excitonic insulator. Our finding allows us to provide a physical interpretation to the unusual mass enhancement of charge carriers in ZrSiS recently observed experimentally.