Low-lying vibrational states in superconducting κ-(BEDT-TTF)2Cu(NCS)2: Inelastic neutron scattering

We report here two kinds of time-of-flight inelastic-neutron-scattering measurements using LAM-D and LAM-40 spectrometers on an aggregate of randomly oriented single crystals and a piece of single crystal, respectively, of hydrogenated κ-(hg-BEDT-TTF)2 Cu(NCS)2. The generalized partial density-of-states spectrum shows an anomalous enhancement in low-lying energy regime below several meV at low temperatures below Tc. It suggests that low-lying vibrational modes involving protons at terminal ethylenes appear in the superconducting phase.