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.
@article{arxiv.1712.07916,
title = {Excitonic Instability and Pseudogap Formation in Nodal Line Semimetal ZrSiS},
author = {A. N. Rudenko and E. A. Stepanov and A. I. Lichtenstein and M. I. Katsnelson},
journal= {arXiv preprint arXiv:1712.07916},
year = {2018}
}