  We report 51V-NMR study on a high-quality powder sample of volborthite
Cu3V2O7(OH)2/2H2O, a spin-1/2 Heisenberg antiferromagnet on a distorted kagome
lattice formed by isosceles triangles. In the magnetic fields below 4.5 T, a
sharp peak in the nuclear spin-lattice relaxation rate 1/T1 accompanied with
line broadening revealed a magnetic transition near 1 K. The low temperature
phase shows anomalies such as a Lorentzian line shape, a 1/T1 propto T behavior
indicating dense low energy excitations, and a large spin-echo decay rate 1/T2
pointing to unusually slow fluctuations. Another magnetic phase appears above
4.5 T with less anomalous spectral shape and dynamics.
