Phonon-Roton Dispersion Curve

1. Phonon-Roton Excitations of Liquid Helium at Negative PressuresHenry Glyde, University of Delaware, Oscar Vilches, University of Washington,John Larese, University of TennesseeFocused Research Group, Neutron Scattering: DMR-0115663 We have observed the fundamental phonon-roton excitations of superfluid 4He held at negative pressures using neutrons. By stretching liquid 4He between the walls of porous media, we have reached equilibrium negative pressures to – 5 bar. Liquids at negative pressures are of great interest to reveal liquid binding, explore the liquid/gas transition and to study cavitation (bubble formation) and neutron scattering is now a new tool in their study. Phys. Rev. Lett. (in press) (2004) Phonon-Roton Dispersion Curve

2. Phonon-Roton Excitations of Liquid Helium at Negative Pressures Henry Glyde, University of Delaware, Oscar Vilches, University of Washington, John Larese, University of Tennessee Focused Research Group, Neutron Scattering: DMR-0115663 The FRG currently has two post doctoral associates, one stationed at the Institut Laue Langevin, Grenoble and the other at the ISIS neutron Facility, UK, and eleven graduate students. Educational goals are to train young scientists in neutron scattering in preparation for the Spallation Neutron Source (SNS) coming on line at Oak Ridge National laboratory and to provide an international research experience for graduate students. Former post docs, Richard Azuah, Olivier Plantevin and Francesco Albergamo (opposite) are now at NIST, Gaithersburg and ESRF, Grenoble and continue to collaborate with the FRG.