Berlin 2012 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 31: Phase Transitions and Critical Phenomena
DY 31.1: Topical Talk
Friday, March 30, 2012, 09:30–10:00, MA 004
Pair Superfluidity of Constrained Bosons in Two Dimensions — •Stefan Wessel1 and Lars Bonnes2 — 1RWTH Aachen University, Germany — 2University of Innsbruck, Austria
Bose gases with attractive interactions can form two different superfluid phases. Besides the conventional (atomic) superfluid, a molecular superfluid of boson pairs can form, with exhibits half-vortex topological defects. To prevent the attractive Bose gas from collapse, a scenario has been recently been proposed, where the particles are constrained to an optical lattice and furthermore subject to strong three-body losses, that project out triple occupancy on each lattice site. Employing quantum Monte Carlo simulations, we study the quantum phase transition between these atomic and dimer superfluids. Evidence is provided for the existence of a tricritical point along the saturation transition line, where the transition changes from being first-order to a continuous transition of the dilute bose gas of holes. We show that the thermal disintegration of the pair superfluidity is governed by the proliferation of fractional half-vortices leading to an Berezinskii-Kosterlitz-Thousless transition with an anomalous stiffness jump. 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.