Neutron Scattering Study on a S=1/2 Quasi-two-dimensional Magnet (CuCl)LaNb$_2$O$_7$

Magnetic properties of polycrystalline (CuCl)LaNb$_2$O$_7$ were studied by magnetic susceptibility and neutron scattering measurements. Magnetic susceptibility exhibits a broad maximum around 16 K, followed by a rapid decrease with decreasing temperature. Powder neutron diffraction measurement provides no evidence of magnetic ordering down to 1.5 K. Furthermore inelastic neutron scattering measurement shows magnetic excitation at around 2.1 meV. These experimental results suggest that this compound has a spin-singlet ground state which is separated from the excited state with a finite-energy gap.