EXCITATIONS IN A THIN LIQUID-HE-4 FILM FROM INELASTIC NEUTRON-SCATTERING

Citation
Be. Clements et al., EXCITATIONS IN A THIN LIQUID-HE-4 FILM FROM INELASTIC NEUTRON-SCATTERING, Physical review. B, Condensed matter, 53(18), 1996, pp. 12242-12252
Citations number
31
Categorie Soggetti
Physics, Condensed Matter
ISSN journal
01631829
Volume
53
Issue
18
Year of publication
1996
Pages
12242 - 12252
Database
ISI
SICI code
0163-1829(1996)53:18<12242:EIATLF>2.0.ZU;2-Z
Abstract
We perform a thorough analysis of the experimental dynamic structure f unction measured by inelastic neutron scattering for a low-temperature (T=0.65 K) four-layer liquid He-4 film. The results are interpreted i n light of recent theoretical calculations of the (nonvortex) excitati ons in thin liquid Bose films. The experimental system consists of fou r outer liquid layers, adsorbed to two solid inner He-4 layers, which are themselves adsorbed to a graphite substrate. Relatively intense su rface (ripplon) and bulklike modes are observed. The analysis of the e xperimental data gives strong evidence for still other modes and suppo rts the long-standing theoretical predictions of layerlike modes (laye r phonons) associated with excitations propagating primarily within th e liquid layers comprising the film. The results of the analysis are c onsistent with the occurrence of level crossings between modes, and th e existence of a layer modes for which the theory predicts will propag ate in the vicinity of the solid-liquid interface. The theory and expe riment agree on the detailed nature of the ripplon; its dispersion at low momenta, its fall off in intensity at intermediate momenta, and th e level crossings at high momentum. Similar to experiment, the theory yields an intense mode in the maxon-roton region which is interpreted as the formation of the bulklike excitation.