# Gapped spin-1/2 spinon excitations in a new kagome quantum spin liquid compound Cu$_3$Zn(OH)$_6$FBr

## TL;DR

This study presents evidence of gapped spin-1/2 spinon excitations in a new kagome quantum spin liquid compound, demonstrating spin fractionalization and topological order through low-temperature magnetic measurements.

## Contribution

The paper reports the discovery of a new kagome quantum spin liquid compound exhibiting spin fractionalization and a low-temperature spin gap, with experimental evidence supporting topological order.

## Key findings

- No phase transition down to 50 mK.
- Observation of a low-temperature spin gap.
- Magnetic field dependence consistent with spinon excitations.

## Abstract

We report a new kagome quantum spin liquid candidate Cu$_3$Zn(OH)$_6$FBr, which does not experience any phase transition down to 50 mK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature ($\sim$ 200 K). A clear gap opening at low temperature is observed in the uniform spin susceptibility obtained from $^{19}$F nuclear magnetic resonance measurements. We observe the characteristic magnetic field dependence of the gap as expected for fractionalized spin-1/2 spinon excitations. Our experimental results provide firm evidence for spin fractionalization in a topologically ordered spin system, resembling charge fractionalization in the fractional quantum Hall state.