We consider a two-leg Bose-Hubbard ladder in the presence of a magnetic flux. We make use of Gross-Pitaevskii, Bogoliubov, bosonization, and renormalization group approaches to reveal a structure of ground-state phase diagrams in a weak-coupling regime relevant to cold atom experiments. It is found that, except for a certain flux φ=π, the system shows different properties as changing hoppings, which also leads to a quantum phase transition similar to the ferromagnetic XXZ model. This implies that population-imbalance instability occurs for certain parameter regimes. On the other hand, for φ=π, it is shown that an umklapp process caused by commensurability of a magnetic flux stabilizes a superfluid with chirality and the system does not experience such a phase transition.
|Physical Review A - Atomic, Molecular, and Optical Physics
|Published - 2015 7月 21
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