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Interacting bosons on a two-leg ladder: Vortex-lattice phases and spontaneous current reversal

Sebastian Greschner, Hannover University

04.05.2015 at 16:00 

In this talk I will present the rich physics of ultra-cold bosons in ladders with an externally applied synthetic magnetic field.
Our detailed numerical studies, motivated by recent experimental realizations such as [Atala et al., Nature Phys. {\bf 10}, 588 (2014)], unveil a wealth of quantum phases for different interaction strengths: In the regime of  hardcore repulsive bosons we observe Meissner and vortex liquid phases both in the superfluid and in the Mott insulator regime. For the case of moderate and weak interaction strengths we show how additionally for certain commensurate vortex-densities vortex-lattice phases form and a superfluid phase with spontaneously imbalanced particle number between the legs of the ladder, the so-called biased leg phase, emerges.
The vortex-lattice phases with a spontaneously broken translational symmetry may exhibit a characteristic and counter-intuitive many-body feature: At sufficiently low temperatures and for arbitrary weak interactions strengths the edge current may reverse its direction. I will present a careful analysis and explanation of this current reversal phenomenon in both the experimentally relevant weak-coupling high-density regime as well as the case of moderate interactions.
In the last part of my talk I will point out scenarios for the realization and study of density-dependent synthetic magnetism, in which there is a feedback of the atoms on the field.

H 537, Schellingstr. 4, V