Vesignieite BaCu_3V_2O_8(OH)_2 as a Candidate Spin-1/2 Kagome Antiferromagnet(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

A polycrystalline sample of vesignieite BaCu_3V_2O_8(OH)_2 comprising a nearly ideal kagome lattice composed of Cu^<2+> ions carrying spin 1/2 has been synthesized and studied by magnetization and heat capacity measurements. Magnetic susceptibility shows a neither long range order, a spin glass transition nor a spin gap down to 2K, in spite of a moderately strong antiferromagnetic interaction of J/k_B=53K between nearest-neighbor spins. A broad peak observed at a temperature corresponding to 0.4J in intrinsic magnetic susceptibility indicates a marked development of the short-range order. The ground state of vesignieite is probably a gapless spin liquid or is accompanied by a very small gap less than 〜J/30.