Excitonic instability and unconventional pairing in the nodal-line materials ZrSiS and ZrSiSe

TL;DR

This study uses a functional renormalization group approach to analyze interaction-driven instabilities in ZrSiS and ZrSiSe, confirming excitonic instability in ZrSiS and suggesting potential for unconventional superconductivity in ZrSiSe.

Contribution

It applies fRG to a realistic model of ZrSiS and ZrSiSe, identifying excitonic and superconducting instabilities based on ab initio parameters.

Findings

Excitonic instability confirmed in ZrSiS.

Energy scale matches experimental mass enhancement.

Potential for d-wave superconductivity in ZrSiSe.

Abstract

We use a functional renormalization group (fRG) approach to investigate potential interaction-induced instabilities in a two-dimensional model for the Dirac nodal-line materials ZrSiS and ZrSiSe employing model parameters derived from {\it ab initio} calculations. Our results confirm that the excitonic instability recently found in random-phase approximation for ZrSiS is indeed the leading instability. In the simplest modeling, spin- and charge-excitonic states are degenerate. Beyond this, we show that the fRG analysis produces an energy scale for the onset of the instability in good agreement with the experimentally observed mass enhancement. Additionally, by exploring the parameter space of the model we find that reducing the band splitting increases the instability scale and gives the chance to drive the system into an unconventional superconducting pairing state. The model parameters for the case of the structurally similar material ZrSiSe suggest the $d$-wave superconducting state as the leading instability with a very small critical scale.