Berlin 2012 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 30: Matter At Low Temperature: Quantum Liquids, Bose-Einstein Condensates, Ultra-cold Atoms, ... 1
TT 30.11: Talk
Wednesday, March 28, 2012, 18:15–18:30, H 3005
Half-Vortex Unbinding and Ising Transition in Two-Dimensional Superfluids — •Lars Bonnes1,2 and Stefan Wessel3 — 1Institut für Theoretische Physik, Universität Innsbruck, Österreich — 2Institut für Theoretische Physik III, Universität Stuttgart — 3Institut für Theoretische Festkörperphysik, RWTH Aachen
We analyze the thermodynamics of the atomic and (nematic) pair superfluids appearing in the attractive two-dimensional Bose-Hubbard model with a three-body hard-core constraint that has been derived as an effective model for cold atoms subject to strong three-body losses in optical lattices. We show that the thermal disintegration of the pair superfluidity is governed by the proliferation of fractional half-vortices leading to an unconventional Berezinskii-Kosterlitz-Thousless transition. In addition to the (conventional) Berezinskii-Kosterlitz-Thousless transition out of the atomic superfluid, we furthermore identify a direct thermal phase transition separating the pair and the atomic superfluid phases, and show that this transition is continuous with critical scaling exponents consistent with those of the two-dimensional Ising universality class. Our results make a direct connection between the partial loss of quasi long-range order at the Ising transition between the two superfluids and the parity selection of the atomic winding number fluctuations that distinguish the atomic and pair superfluid.