Unification of BKT and BEC phase transiton in a trapped two-dimensional Bose-gas

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• Dr Martin Robert de Saint Vincent, Cavendish Laboratory Cambridge
• Thursday 05 February 2015, 13:45-15:00
• Theory Library.

If you have a question about this talk, please contact Kevin Ralley.

Coherence and superfluidity in quantum fluids can emerge, typically together, from a variety of mechanisms. Finite size two-dimensional (2d) Bose gases present a subtle interplay between Bose- Einstein Condensation, driven by quantum statistics, and the interaction-driven Berezinskii- Kosterlitz-Thouless (BKT) phase transition, at which free vortices become suppressed and quasi- long range order emerges. To explore the respective roles of quantum statistics and interactions, we study experimentally the critical point for the emergence of coherence in a harmonically trapped 2d Bose gas with tunable interactions. Over a wide range of interaction strengths we find excellent agreement with predictions based on the BKT theory of 2d superfluidity. This allows us to quantitatively show, without any free parameters, that the interaction-driven BKT transition smoothly converges onto the purely statistical Bose-Einstein condensation (BEC) transition in the limit of vanishing interactions.

This talk is part of the Theoretical Physics Seminars series.

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