|  Superfluidity | 
In General
  > s.a. bose-einstein condensation; particle statistics.
  *  Properties: Superfluids exhibit zero
    viscosity, and quantized vortices when rotated or subject to a temperature gradient.
  *  Method: Study using second-waves,
    regions with different concentrations of ordinary/superfluid components.
  @ General references: Feynman RMP(57);
    Khalatnikov 65;
    SA(76)dec;
    Collins PT(92)jun;
    news pn(96)oct;
    Guénault 03;
    Adams & Bry PhyA(04);
    Annett 04 [intro];
    Brandão NJP(05) [order parameter and entanglement];
    Balibar CP(07);
    Pilati et al PRL(08) [critical T, 2D and 3D];
    Yu AP(08) [as a Bose exchange effect];
    Sewell & Wreszinski JPA(09) [mathematical theory];
    Dupuis PRL(09) [unified picture];
    Roberts CP(09) [drag forces on moving objects];
    Tsubota et al PRP(13) [rev];
    Andrianopoli PLB(14) [field-theoretical description];
    Schmitt LNP-a1404 [intro, field-theoretical approach and applications];
    Wreszinski a1506-conf [rev].
  @ History: Andronikashvili 90;
    Donnelly PT(95)jul;
    Balibar phy/06,
    Griffin pw(08)aug [discovery];
    Kadanoff JSP(13)-a1303 [Lev Landau and John Bardeen, and the importance of the condensate].
Types / Examples > s.a. knots [quantum knots in a superfluid];
  Quasiparticles; sound; turbulence.
  *  Helium: Known and studied since 1938;
    In 4He, pairs of atoms condense into a macroscopically
    coherent quantum state (Bose-Einstein condensation) at 2.18 K, which manifests itself
    as a frictionless fluid; In 3He, the situation is not
    so simple, and is usually described by the two-fluid model invented by Laszo Tisza and
    Lev Landau in the late 1930s; He II (0 to 2.172 K) is a superfluid, highly heat-conductive
    by friction-free convection and described by the Euler equation for an ideal inviscid
    fluid; He I (2.172 to 4.2 K) is an ordinary fluid, governed by the Navier–Stokes
    equation for viscous flow; The superfluid can also be treated, as proposed by Fritz
    London, Lars Onsager, and Richard Feynman, as a macroscopic quantum state characterized
    by a complex wavefunction.
  *  Other examples: 2005, Evidence from solid hydrogen
    [@ news pn(05)mar].
  *  In curved spacetime: Superfluids in intense
    gravitational fields are assumed to be present in neutron star and quark star cores.
  @ 3He:
    Bunkov et al PRL(00) [sets of 4 atoms?];
    Finne et al Nat(03)aug
    + pn(03)aug [criterion for the onset of turbulence];
    Volovik JLTP(08)cm/07 [history];
    Ma & Wang PhyA(08) [new models];
    Golovko a1103 [leaking out of an open container];
    Volovik & Krusius Phy(12) [coherent quantum states of different chirality].
  @ 4He:
    Pollet et al PRL(08),
    comment Balibar Phy(08) [solid];
    Guo et al PRL(10)
    + Barenghi Phy(10)
      [visualization of turbulent behavior of normal-fluid component];
    news sn(17)mar [simulations and area law for entropy];
    > s.a. condensed matter [supersolid].
  @ In general relativity and cosmology: Zurek Nat(85)oct [topological defects in cosmology and superfluidity];
    Carter gq/99-ln [vortex dynamics],
    G&C(00)ap [neutron stars];
    Casini & Montemayor gq/99 [covariant];
    Volovik PRP(01)gq/00 [analogs];
    Garcia de Andrade gq/05 [with torsion];
    Villegas a1511 [effect of spacetime curvature];
    Huang 16 [the universe as a quantum superfluid].
  @ Examples: Donnelly pw(97)feb [rotons];
    Kapusta PRL(04)ht [for Dirac neutrinos];
    Bulgac et al PRL(06) [spin-1/2 fermions];
    Kastrinakis AP(14)-a0901 [new states];
    news PhysOrg(10)oct [light];
    Enss Phy(14)
      [transition between bosonic and fermionic superfluidity in 2D quantum fluids of ultracold atoms];
    López et al PRL(15) [using self-propelling bacteria];
    Singh & Mathey a2010 [2D ultracold Bose gas].
  @ Applications: Sato & Packard PT(12)oct [superfluid He quantum interference device, SHeQUID]. 
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