title: Evidence for a common physical origin of the Landau and BEC theories of superfluidity.
abstract: There are two renowned theories of superfluidity in liquid (4)He, quite different and each with specific domains of application. In the first, the Landau theory, superflow follows from the existence of a well-defined collective mode supported by dense liquid (4)He, the phonon-roton mode. In the second, superflow is a manifestation of Bose-Einstein condensation (BEC) and phase coherence in the liquid. We present combined measurements of superfluidity, BEC and phonon-roton (P-R) modes in liquid (4)He confined in the porous medium MCM-41. The results integrate the two theories by showing that well-defined P-R modes exist where there is BEC. The two are common properties of a Bose condensed liquid and either can be used as a basis of a theory of superfluidity. In addition, the confinement and disorder suppresses the critical temperature for superfluidity, Tc, below that for BEC creating a localized BEC "phase" consisting of islands of BEC and P-R modes. This phase is much like the pseudogap phase in the cuprate superconductors.
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: S O
authors.initials: SO
authors.lastname: Diallo
authors.affiliation: NIST Center for Neutron Research, Gaithersburg, Maryland 20899-8562, USA and Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742-2115, USA.
authors.forename: R T
authors.initials: RT
authors.lastname: Azuah
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Abernathy
authors.affiliation: Department of Engineering Science, University of Electro-Communications, Chofu, Tokyo 182-8585, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Taniguchi
authors.affiliation: Department of Engineering Science, University of Electro-Communications, Chofu, Tokyo 182-8585, Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: Institut Néel, CNRS-UJF, BP 166, 38042 Grenoble Cedex 9, France.
authors.forename: Jacques
authors.initials: J
authors.lastname: Bossy
authors.affiliation: Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716-2593, USA.
authors.forename: N
authors.initials: N
authors.lastname: Mulders
authors.affiliation: Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716-2593, USA.
authors.forename: H R
authors.initials: HR
authors.lastname: Glyde