How supersolids melt: vortices near a high-symmetry phase coexistence point.

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• Chris Hooley - Scottish Universities Physics Alliance (SUPA), University of St Andrews
• Wednesday 20 November 2013, 11:15-12:15
• Mott Seminar Room (531), Cavendish Laboratory, Department of Physics.

If you have a question about this talk, please contact Michael Sutherland.

According to the Mermin-Wagner theorem, superfluidity in two dimensions (e.g. a thin film) ought to be impossible. However, superfluid response in such films is routinely seen in experiments. The solution of this apparent contradiction is that the film is not showing true long-range order (which would indeed be impossible), but instead quasi-long-range order: superfluid phase coherence decays with distance, but only in a power-law fashion, which is enough to preserve macroscopic superfluid behaviour.

The way in which this quasi-long-range order eventually goes away is even more fascinating: it happens by a proliferation of free vortices, as explained by Berezinskii, and Kosterlitz and Thouless – collectively known as BKT - in the 1970s. But what becomes of this BKT transition when 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 various experiments involving cold atomic gases. I shall present some of our recent results on this topic, as well as outlining some of the puzzles that remain unresolved.

This talk is part of the Quantum Matter Seminar series.

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• All Cavendish Laboratory Seminars
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• Mott Seminar Room (531), Cavendish Laboratory, Department of Physics
• Neurons, Fake News, DNA and your iPhone: The Mathematics of Information
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