Observation of a new excitation in bcc solid 4He by inelastic neutron scattering

TL;DR

This paper reports the discovery of a new 'optic-like' excitation mode in bcc solid helium-4 using inelastic neutron scattering, suggesting localized excitations unique to quantum solids.

Contribution

It presents the observation of a previously unreported excitation mode in bcc solid 4He, expanding understanding of quantum solid excitations.

Findings

Discovery of a new 'optic-like' mode in bcc solid 4He

Mode observed along the [110] direction

Implication of localized excitations in quantum solids

Abstract

We report neutron scattering measurements of the phonons in bcc solid 4He. In general, only 3 accoustic phonon branches should exist in a monoatomic cubic crystal. In addition to these phonon branches, we found a new ''optic-like'' mode along the [110] direction. One possible interpretation of this new mode is in terms of localized excitations unique to a quantum solid.