BiCu${}_2$VO${}_6$: a new narrow-band spin-gap material

A new spin-ladder family material BiCu${}_2$VO${}_6$ is studied by means of the magnetic susceptibility, heat capacity and neutron inelastic scattering measurements on powder sample. Singlet ground state and a finite spin gap are confirmed by thermal-activated type susceptibility and by distinct peak at 16 meV in spin excitation. Triple narrow band structure in spin excitation spectrum, probably due to complex crystal structure, is observed and the possibility of weakly-interacting spin-cluster system is discussed.