Quantum tricriticality and bright-like dark solitons in binary Bose mixtures in optical lattices
Recent experiments on ultracold atoms in optical lattices have observed quantum criticality accompanying the second-order quantum phase transition between vacuum and superfluid, providing new opportunities for studying quantum criticality in optical-lattice systems. Motivated by the experimental development, we study quantum criticality near a tricritical point (TCP) in the two-component Bose-Hubbard model on square lattices. The existence of quantum TCP on a boundary of superfluid-insulator transition is confirmed by quantum Monte Carlo simulations. Moreover, we analytically derive the quantum tricritical scaling on the basis of an effective field theory. We find two significant features of the quantum tricriticality, that are its characteristic chemical potential dependence of the superfluid transition temperature and a strong density fluctuation. We also analyze soliton solutions of a superfluid state to find a bright-like dark soliton, which has a non-vanishing density dip and no pi phase kink even in the case of a standing soliton. We suggest that these features are directly observable in existing experimental setups of Bose-Bose mixtures in optical lattices.
Host: Charles Clark