Field-Induced Freezing of a Quantum Spin Liquid on the Kagome Lattice

TL;DR

This study uses 17O NMR to reveal a magnetic field-induced transition from a gapless quantum spin liquid to a spin-solid phase in Herbertsmithite, indicating a quantum critical point at low magnetic field.

Contribution

It provides experimental evidence of a field-induced phase transition and quantum criticality in a kagome antiferromagnet, supporting theoretical predictions involving Dzyaloshinskii-Moriya interactions.

Findings

Discovery of a spin-solid phase induced by magnetic field

Identification of a quantum critical point at ~1.55T

Observation of gapped excitations in the high-field phase

Abstract

We report 17O NMR measurements in the S=1/2 Cu2+ kagome antiferromagnet Herbertsmithite ZnCu3(OH)6Cl2 down to 45mK in magnetic fields ranging from 2T to 12T. While Herbertsmithite displays a gapless spin-liquid behavior in zero field, we uncover an instability toward a spin-solid phase at sub-kelvin temperature induced by an applied magnetic field. The latter phase shows largely suppressed moments $\lesssim 0.1\muB$ and gapped excitations. The H-T phase diagram suggests the existence of a quantum critical point at the small but finite magnetic field mu0 Hc=1.55(25)T. We discuss this finding in light of the perturbative Dzyaloshinskii-Moriya interaction which was theoretically proposed to sustain a quantum critical regime for the quantum kagome Heisenberg antiferromagnet model.