Observation of a new excitation in bcc 4He by inelastic neutron scattering -: art. no. 195301

We report neutron-scattering measurements of the phonons in bcc solid He-4 . In general, only three acoustic phonon branches should exist in a monatomic cubic crystal. In addition to these phonon branches, we found a new opticlike mode along the [110] direction. One possible interpretation of this new mode is in terms of localized excitations unique to a quantum solid.