Quantum Criticality of Excitonic Insulating Transition in Nodal Line Semimetal ZrSiS

TL;DR

This paper investigates the quantum critical behavior in the topological nodal line semimetal ZrSiS, revealing how excitonic fluctuations near a quantum critical point lead to fermion mass enhancement while maintaining Fermi liquid properties.

Contribution

It demonstrates that ZrSiS is close to a quantum critical point, explaining its mass enhancement through excitonic quantum fluctuations and establishing it as a strongly correlated Fermi liquid.

Findings

Fermion velocities are significantly reduced near the critical point.

Mass enhancement is explained by excitonic quantum fluctuations.

ZrSiS remains a strongly correlated Fermi liquid at low energies.

Abstract

Pezzini et al. reported an unconventional mass enhancement in topological nodal line semimetal ZrSiS (Nat. Phys. 14, 178 (2018), whose origin remains puzzling. In this material, strong short-range interactions might induce excitonic particle-hole pairs. Here we study the renormalization of fermion velocities and find that the mass enhancement in ZrSiS can be well understood if we suppose that ZrSiS is close to the quantum critical point between semimetal and excitonic insulator. Near this quantum critical point, the fermion velocities are considerably reduced by excitonic quantum fluctuation, leading to fermion mass enhancement. The quasiparticle residue is suppressed as the energy decreases but is finite at zero energy. This indicates that ZrSiS is a strongly correlated Fermi liquid, and explains why the mass enhancement is weaker than non-Fermi liquids. Our results suggest that ZrSiS is a rare example of 3D topological semimetal exhibiting unusual quantum criticality.