Browsing by Author "Eltsov, V.B."

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  • Composite defect extends analogy between cosmology and 3He
    (2000) Eltsov, V.B.; Kibble, T.W.B.; Krusius, M.; Ruutu, V.M.H.; Volovik, G.E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Spin-mass vortices have been observed to form in rotating superfluid 3He−B, following the absorption of a thermal neutron and a rapid transition from the normal to the superfluid state. The spin-mass vortex is a composite defect which consists of a planar soliton (wall) which terminates on a linear core (string). This observation fits well within the framework of a cosmological scenario for defect formation, known as the Kibble-Zurek mechanism. It suggests that in the early Universe analogous cosmological defects might have formed.
  • Defect formation in Quench-cooled superfluid phase transition
    (1998) Ruutu, V.M.; Eltsov, V.B.; Krusius, M.; Makhlin, Yu.G.; Plaçais, B.; Volovik, G.E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We use neutron absorption in rotating 3He−B to heat locally a ∼100−μm−size volume into normal phase. When the heated region cools back in microseconds, vortex lines are formed. We record with NMR the number of lines vs the applied superflow velocity and compare to the Kibble-Zurek theory of vortex-loop freeze-out from a random network of defects. The measurements confirm the calculated loop-size distribution and indicate that the superfluid state itself forms as a patchwork of competing A− and B−phase blobs. The consequences to the A→B transition in supercooled 3He−A are discussed.
  • Energy and angular momentum balance in wall-bounded quantum turbulence at very low temperatures
    (2013) Hosio, J.J.; Eltsov, V.B.; Heikkinen, P.J.; Hänninen, R.; Krusius, M.; "L'vov", V.S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A superfluid in the absence of a viscous normal component should be the best realization of an ideal inviscid Euler fluid. As expressed by d’Alembert’s famous paradox, an ideal fluid does not drag on bodies past which it flows, or in other words it does not exchange momentum with them. In addition, the flow of an ideal fluid does not dissipate kinetic energy. Here we study experimentally whether these properties apply to the flow of superfluid 3He-B in a rotating cylinder at low temperatures. It is found that ideal behaviour is broken by quantum turbulence, which leads to substantial energy dissipation, as was also observed earlier. Remarkably, the angular momentum exchange between the superfluid and its container approaches nearly ideal behaviour, as the drag almost disappears in the zero-temperature limit. Here the mismatch between energy and angular momentum transfer results in a new physical situation, with severe implications on the flow dynamics.
  • Propagation of thermal excitations in a cluster of vortices in superfluid 3He-B
    (2011) Hosio, J.J.; Eltsov, V.B.; de Graaf, R.; Krusius, M.; Mäkinen, J.; Schmoranzer, D.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Quasiparticle-scattering measurements of laminar and turbulent vortex flow in the spin-down of superfluid 3He-B
    (2012) Hosio, J.J.; Eltsov, V.B.; Krusius, M.; Mäkinen, J.T.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Self-trapping of magnon Bose-Einstein Condensates in the ground state and on excited levels: from harmonic to box confinement
    (2012) Autti, S.; Bunkov, Yu.M.; Eltsov, V.B.; Heikkinen, P.J.; Hosio, J.J.; Hunger, P.; Krusius, M.; Volovik, G.E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Long-lived coherent spin precession of 3He−B at low temperatures around 0.2Tc is a manifestation of Bose-Einstein condensation of spin-wave excitations or magnons in a magnetic trap which is formed by the order-parameter texture and can be manipulated experimentally. When the number of magnons increases, the orbital texture reorients under the influence of the spin-orbit interaction and the profile of the trap gradually changes from harmonic to a square well, with walls almost impenetrable to magnons. This is the first experimental example of Bose condensation in a box. By selective rf pumping the trap can be populated with a ground-state condensate or one at any of the excited energy levels. In the latter case the ground state is simultaneously populated by relaxation from the exited level, forming a system of two coexisting condensates.
  • Superflow-stabilized nonlinear NMR in rotating 3He-B
    (1999) Dmitriev, V.V.; Eltsov, V.B.; Krusius, M.; Ruohio, J.J.; Volovik, G.E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Nonlinear spin precession has been observed in 3He−B in large counterflow of the normal and superfluid fractions. The new precessing state is stabilized at a high rf excitation level and displays frequency-locked precession over a large range of frequency shifts, with the magnitude of magnetization at its equilibrium value. Comparison to analytical and numerical calculation indicates that in this state the orbital angular momentum L of the Cooper pairs is oriented transverse to the external magnetic field in a “non-Leggett” configuration with broken spin-orbit coupling. The resonance shift depends on the tipping angle θ of the magnetization as ω−ωL=(Ω2B/2ωL)(cosθ−1/5). The phase diagram of the precessing modes with arbitrary orientation of L is constructed.
  • Superfluid vortex front at T -> 0: decoupling from the reference frame
    (2011) Hosio, J.J.; Eltsov, V.B.; de Graaf, R.; Heikkinen, P.J.; Hänninen, R.; Krusius, M.; "L'vov", V.S.; Volovik, G.E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Steady-state turbulent motion is created in superfluid 3He−B at low temperatures in the form of a turbulent vortex front, which moves axially along a rotating cylindrical container of 3He−B and replaces vortex-free flow with vortex lines at constant density. We present the first measurements on the thermal signal from dissipation as a function of time, recorded at 0.2Tc during the front motion, which is monitored using NMR techniques. Both the measurements and the numerical calculations of the vortex dynamics show that at low temperatures the density of the propagating vortices falls well below the equilibrium value, i.e., the superfluid rotates at a smaller angular velocity than the container. This is the first evidence for the decoupling of the superfluid from the container reference frame in the zero-temperature limit.