Phonons, rotons, and layer modes of liquid 4He in aerogel

Zero sound and atomiclike excitations: The nature of phonons and rotons in liquid 4He.

4He Films on Graphite Studied by Neutron Scattering*

The properties of 4He films adsorbed on graphite have been studied by neutron scattering. In particular excitations of the commensurate phase of the monolayer are discussed. The first two adsorbed layers are solid and the next ones stay liquid. At the boundaries of the superfluid film excitations could be studied. Also the phonons, maxon and rotons of the film are investigated. An explanation o...

Excitations of metastable superfluid 4He at pressures up to 40 bars.

Neutron scattering measurements of the fundamental excitations of liquid 4He confined in 44 A pore diameter gelsil glass at pressures up to 40 bars in the wave vector range 0.4<Q<2.3 A(-1) are reported. Above 25.3 bars and at low temperature (T=0.4 K) the characteristic phonon-roton mode of superfluid 4He is no longer observed as a well-defined mode in the phonon-maxon region (0.4<Q<1.6 A(-1))....

Localized Bose-Einstein condensation in disordered liquid 4He films

We present neutron scattering measurements of the phonon-roton and layer modes of liquid helium films adsorbed in 25-Å pore diameter gelsil as a function of temperature. The goal is to determine whether the well-defined phonon-roton and layer modes observed at low temperature at partial fillings of the porous media persist as well-defined modes at higher temperatures above the superfluid phase,...

Excitations in a thin liquid 4He film from inelastic neutron scattering.

We perform a thorough analysis of the experimental dynamic structure function measured by inelastic neutron scattering for a low-temperature (T50.65 K! four-layer liquid He film. The results are interpreted in light of recent theoretical calculations of the ~nonvortex! excitations in thin liquid Bose films. The experimental system consists of four outer liquid layers, adsorbed to two solid inne...