Phonon-Phonon Interaction in Liquid Helium II

Nanomechanical vibrating wire resonator for phonon spectroscopy in liquid helium

We demonstrate how to machine a vibrating wire resonator for ultrasonic excitations in gaseous and liquid helium. This novel resonator is designed as a nanoscopic mechanically flexible bridge machined out of a semiconductor/metal hybrid. Quenching of the mechanical resonance around 100 MHz in gaseous and liquid 4He at 4.2 K is shown. Vibrating wire resonators (VWRs) are standard bolometers for ...

A NUMERICAL RENORMALIZATION GROUP APPROACH FOR AN ELECTRON-PHONON INTERACTION

A finite chain calculation in terms of Hubbard X-operators is explored by setting up a vibronic Harniltonian. The model conveniently transformed into a form so that in the case of strong coupling a numerical renormalization group approach is applicable. To test the technique, a one particle Green function is calculated for the model Harniltonian

Exciton-phonon interaction in GaSe

Phonon-roton modes and localized Bose-Einstein condensation in liquid helium under pressure in nanoporous media.

We show, using inelastic neutron scattering, that liquid helium in porous media, two gelsils and MCM-41, supports a phonon-roton mode up to a pressure of 36-37 bars only. Modes having the highest energy ("maxons") broaden and become unobservable at the lowest pressures (p approximately 26 bars) while rotons survive to the highest pressure. By comparing with the superfluid density observed by Ya...

Saturation Effects in the Phonon Reflection at a Quartz-Liquid Helium Interface*

The reflection coefficient of longitudinal 25-GHz phonons at a quartz-liquid 4He interface was measured for various phonon intensities. For thoroughly cleaned quartz surfaces a reflection coefficient of I independent of the incident intensity was found. When the sample was covered with a thin hydrocarbon film, however, the reflection coefficient dropped by typically 5-10% when the phonon intens...