Speaker:
Paul M. Goldbart, Department of Physics, University of Illinois at
Urbana-Champaign

Title:
Synchronized phase-slippage and the flow of superfluid helium-four
through nano-aperture arrays

Abstract:
Recent experiments by the U.C. Berkeley group [1] have explored the
dynamics of helium-four superflow through an array of several
thousand nanosized apertures.  These experiments have found that, as
the temperature is lowered, phase-slippage in the apertures changes
its character, from synchronous to asynchronous.  We have constructed
a model of superflow through arrays of nanosize apertures which aims
to account for these findings [2].  It has two basic ingredients: (a)
disorder, associated with each aperture having its own random
critical velocity; and (b) effective inter-aperture coupling,
mediated through the bulk superfluid.  It predicts that synchronicity
of the phase-slips is lost at lower temperatures, due to an effective
broadening of the distribution of the critical velocities.  It also
predicts that, as the disorder becomes weak, there is a
nonequilibrium phase transition to a regime in which the
inter-aperture couplings induce macroscopic, synchronous, system-wide
phase-slip avalanche events.  If time permits, we shall look at some
of the many connections between avalanche phenomena in superfluid
helium and those arising in other settings, including magnetism,
charge-density wave materials, and seismology.

[1] Y. Sato, E. Hoskinson and R. E. Packard, Transition from
synchronous to asynchronous superfluid phase slippage in an aperture
array, Phys. Rev. B 74, 144502 (2006).
[2] D. Pekker, R. Barankov and P.M. Goldbart, Phase-slip avalanches
in the superflow of helium-four through arrays of nanosize apertures,
Phys. Rev. Lett. 98, 175301 (2007).






Piers Coleman wrote:

      Dear Paul,

          Somehow, Aspen passed so quickly, that we never
      really had chance to talk there.  Well - I hope your trip
      to Rutgers this Fall will help to fix this.

          Could you please let me know the title for your
      Rutgers seminar on Nov 27th, asap, plus an abstract.  If
      you have chance to book your travel soon, please let me
      know which nights you will need accomodation in New
      Brunswick.

           Cheers, Piers

      ===========================================================================
      Piers Coleman
      Professor
      Dept of Physics and Astronomy        Tel:  732-445-5082
      Rutgers University            Fax:  732-445-4400
      136 Frelinghuysen Road            Room: 268 Serin
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      www.physics.rutgers.edu/~coleman/
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