Spin dynamics in the S = 1/2 quantum kagome compound vesignieite, Cu3Ba(VO5H)2

We report the study of high-quality samples of the frustrated S = 1 2 kagome antiferromagnet vesignieite, Cu 3 Ba(VO 5 H) 2 . Neutron powder diffraction measurements evidence the excellence of the kagome lattice and show no sign of a transition to magnetic long-range order. A kink in the susceptibility below T = 9 K is matched to a reduction in paramagnetic-like correlations in the diffraction data and a slowing of the spin dynamics observed by μ SR. Our results point to an exotic quantum state below 9 K with coexistence of both dynamical and small frozen moments ~ 0.1 μ B . We propose that this novel quantum ground state is stabilized by a large Dzyaloshinsky-Moriya interaction