Boson localization and excitations of liquid {sup 4}He confined in gelsil
- European Synchrotron Radiation Facility, Boite Postale 220, F-38043 Grenoble Cedex (France)
- Centre de Recherche sur les Tres Basses Temperatures, CNRS, BP 166, 38042 Grenoble Cedex 9 (France)
- Institut Laue-Langevin, BP 156, 38042 Grenoble (France)
- Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716-2570 (United States)
We present neutron scattering measurements of the phonon-roton (P-R) modes of liquid {sup 4}He at saturated vapor pressure confined in 44 A mean pore diameter gelsil in the wave vector range 0.4{<=}Q{<=}2.15 A{sup -1}. Layer modes, modes which propagate in the liquid layers adjacent to the porous media walls, were also observed at wave vectors in the roton region (Q{approx_equal}1.95 A{sup -1}) but not at Q < or approx. 1.7 A{sup -1}. The first goal is to document the filling dependence of the dynamic response and of the P-R mode energies and widths more systematically than has been done in the past. As the gelsil is filled with {sup 4}He, the P-R and layer modes are first observed at a fractional filling of f=76% at low temperature (T=0.4 K). At fillings f=76%, the P-R mode energies lie below the bulk superfluid {sup 4}He values in the wave vector range 0.4{<=}Q{<=}1.7 A{sup -1}, especially at Q{approx_equal}1.1 A{sup -1}, as observed in helium films. As filling is increased, the intensity in the P-R mode increases markedly and the P-R mode energies move toward bulk superfluid values taking bulk values at full filling. The second goal is to determine the temperature dependence of the intensity in the P-R modes in a media in which the superfluid-normal transition temperature T{sub c}=1.92 K is independently known and lies well below the bulk liquid value T{sub {lambda}}=2.17 K. As temperature is increased, the intensity in the P-R and layer modes decreases. However, a well-defined P-R mode is observed at temperatures up to T{approx_equal}2.15 K, above T{sub c}=1.92 K. Since well-defined modes exist because there is Bose-Einstein condensation (BEC), this suggests that there is BEC above T{sub c}, probably localized. Localized BEC appears to exist up to T{approx_equal}T{sub {lambda}}.
- OSTI ID:
- 21055118
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 76, Issue 6; Other Information: DOI: 10.1103/PhysRevB.76.064503; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BOSE-EINSTEIN CONDENSATION
BOSONS
EXCITATION
FILMS
HELIUM
HELIUM 4
LAYERS
LIQUIDS
NEUTRON DIFFRACTION
PHONONS
POROUS MATERIALS
RINGS
ROTONS
SUPERFLUIDITY
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0065-0273 K
TRANSITION TEMPERATURE
VAPOR PRESSURE
VECTORS