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SUMMARY:How supersolids melt: vortices near a high-symmetry phase coexiste
 nce point. - Chris Hooley - Scottish Universities Physics Alliance (SUPA)\
 , University of St Andrews
DTSTART:20131120T111500Z
DTEND:20131120T121500Z
UID:TALK47186@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:According to the Mermin-Wagner theorem\, superfluidity in two 
 dimensions (e.g. a thin film) ought to be impossible.  However\, superflui
 d response in such films is routinely seen in experiments.  The solution o
 f this apparent contradiction is that the film is not showing true long-ra
 nge order (which would indeed be impossible)\, but instead quasi-long-rang
 e order: superfluid phase coherence decays with distance\, but only in a p
 ower-law fashion\, which is enough to preserve macroscopic superfluid beha
 viour.\n\nThe way in which this quasi-long-range order eventually goes awa
 y is even more fascinating: it happens by a proliferation of free vortices
 \, as explained by Berezinskii\, and Kosterlitz and Thouless - collectivel
 y known as BKT - in the 1970s.  But what becomes of this BKT transition wh
 en the system is near a point of competition with another (non-superfluid)
  phase?  This question is relevant to supersolidity (or the lack thereof) 
 in helium\, as well as to the high-temperature superconductors and to vari
 ous experiments involving cold atomic gases.  I shall present some of our 
 recent results on this topic\, as well as outlining some of the puzzles th
 at remain unresolved.\n
LOCATION:Mott Seminar Room (531)\, Cavendish Laboratory\, Department of Ph
 ysics
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