Dirac spinons intermingled with singlet states in the random kagome antiferromagnet YCu3(OD)6+xBr3−x (x = 0.5)

Abstract

We elucidate the ground state nature and low-energy spin dynamics of the s = 1/2 near-perfect kagome antiferromagnet YCu3(OD)(6+x)Br3-x (x = 0.5) using Cu-63 nuclear quadrupole resonance (NQR) and muon spin relaxation/rotation / rotation (mu SR) techniques. Our combined Cu-63 NQR and mu SR data, along with the inverse Laplace transform analysis, reveal an inhomogeneous ground state comprising the majority of a gapless spin liquid intermingled with a minor fraction of spin singlets with varying energy gaps. Furthermore, the Cu-63 NQR relaxation rate evinces distinct signatures of Dirac spinons, featuring a power-law dependence of 1/T-1 similar to T-eta with eta = 1.35 at temperatures below 0.13 J (congruent to 8 K). Our results demonstrate that a kagome lattice endowed with specific exchange randomness provides a prominent platform for exploring Dirac fermions in magnetic insulators.