2022/03/08 by Jiaming Wang, Weishi Yuan, Philip M. Singer +5 · 1 citation
Physics and Astronomy · #cond-mat.str-el
paper · pdf · doi:10.1038/s41567-021-01310-3
published as Nature Physics 17, 1109-1113 (2021) · 4 Figs
arxiv created 2022/03/08 · arxiv updated 2022/03/09
The kagome Heisenberg antiferromagnet formed by frustrated spins arranged in a lattice of corner-sharing triangles is a prime candidate for hosting a quantum spin liquid (QSL) ground state consisting of entangled spin singlets. But the existence of various competing states makes a convincing theoretical prediction of the QSL ground state difficult, calling for experimental clues from model materials. The kagome lattice materials Zn-barlowite ZnCu3(OD)6FBr and herbertsmithite ZnCu3(OD)6Cl2 do not exhibit long range order, and they are considered the best realizations of the kagome Heisenberg antiferromagnet known to date. Here we use 63Cu nuclear quadrupole resonance combined with the inverse Laplace transform (ILT) to probe locally the inhomogeneity of delicate quantum ground states affected by disorder. We present direct evidence for the gradual emergence of spin singlets with spatially varying excitation gaps, but even at temperatures far below the super-exchange energy scale their fraction is limited to approximately 60% of the total spins. Theoretical models need to incorporate the role of disorder to account for the observed inhomogeneously gapped behaviour.