Anomalous phonon scattering below T-c in (YNi2B2C)-B-11

Inelastic neutron scattering measurements were performed on large volume (similar to 2 cm(3)) single crystals of B-11 substituted intermetallic superconductor (YNi2B2C)-B-11. With decreasing temperature, a gradual softening of a phonon spectrum is observed at around Q = (0.525, 0, 8), similar to the case of LuNi2B2C reported by Dervenagas et al. [Phys. Rev. B 52, R9839 (1995)]. In addition, we discovered that an intense new peak appears below T-c = 14.2 K. With application of magnetic field, however, it is easily suppressed and disappears by H = H-c2 (similar to 4.7 T at T = 5.5 K). These results strongly indicate that this new peak is undoubtedly associated with its superconducting state.