Gapped Spin-1/2 Spinon Excitations in a New Kagome Quantum Spin Liquid Compound Cu₃Zn(OH)₆FBr

Abstract

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