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The origins of superfluidity and superconductivity, whether Bose-Einstein condensation (BEC) or well defined excitations (energy gap), remains to be clarified in many circumstances. We are investigating liquid helium confined to nanoscales in porous media using neutron scattering. We find evidence for both localization of BEC by disorder at SVP [1] and for loss of excitations at higher pressure [2] being responsible for loss of superflow. The schematic figure opposite (top) shows the superfluid phase in porous media. A possible quantum phase transition to normal helium at p ~ 3.2 MPa (32 bars) and T ~ 0 K has been reported [3]. The figure opposite (below) shows loss of phonon-roton modes at p > 25.3 bars [2].

Phase diagram of 4He in porous media (dotted, bulk)

Phonon-roton excitations under pressure

Bose-Einstein condensation, excitations and superfluidityHenry Glyde, University of Delaware, Oscar Vilches, University of Washington,

John Larese, University of Tennessee FRG, Neutron Scattering: DMR-0115663

Bose-Einstein condensation , excitations and superfluidityHenry Glyde, University of Delaware, Oscar Vilches, University of Washington,

John Larese, University of Tennessee FRG, Neutron Scattering: DMR-0115663

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Our neutron scattering program at US and European neutron facilities involves several post doctoral associates, graduate students and undergraduates. It provides training using a wide spectrum of neutron spectrometers at both reactor and spallation based neutron sources as well as an international research experience. Shown opposite (top) is Richard Azuah, formerly a post doc now on staff at the NIST Center for Neutron Research, and Souleymane Omar Diallo (facing laptop), currently a senior graduate student in the group.

Education

[1] H.R. Glyde et al. Phys. Rev. Lett. 84, 2646 (2000); F. Albergamo et al. Phys. Rev. B69, 014514 (2004).

[2] J.V. Pearce et al. Phys. Rev. Lett. 93, 1453303 (2004).

[3] H. Yamamoto et al. Phys. Rev. Lett. 93, 075302 (2004).