# Unconventional mass enhancement around the Dirac nodal loop in ZrSiS

## TL;DR

This study reveals significant mass enhancement and novel correlation effects in the topological semimetal ZrSiS, associated with its Dirac nodal loop, through high-field quantum oscillation experiments.

## Contribution

It provides experimental evidence of enhanced quasiparticle mass and magnetic breakdown phenomena in ZrSiS, highlighting correlation-driven physics in topological nodal loop semimetals.

## Key findings

- Enhanced effective mass near the nodal loop
- Magnetic breakdown orbits with -Berry phase
- Anomalous temperature dependence of orbit amplitudes

## Abstract

The topological properties of fermions arise from their low-energy Dirac-like band dispersion and associated chiralities. Initially confined to points, extensions of the Dirac dispersion to lines and even loops have now been uncovered and semimetals hosting such features have been identified. However, experimental evidence for the enhanced correlation effects predicted to occur in these topological semimetals has been lacking. Here, we report a quantum oscillation study of the nodal loop semimetal ZrSiS in high magnetic fields that reveals significant enhancement in the effective mass of the quasiparticles residing near the nodal loop. Above a threshold field, magnetic breakdown occurs across gaps in the loop structure with orbits that enclose different windings around its vertices, each winding accompanied by an additional \pi-Berry phase. The amplitudes of these breakdown orbits exhibit an anomalous temperature dependence. These findings demonstrate the emergence of novel, correlation-driven physics in ZrSiS associated with the Dirac-like quasiparticles.