Supersolidity of cold-atom Bose-Fermi mixtures in optical lattices

Abstract

We investigate a cold atomic mixture of spinless bosons and fermions in two-dimensional optical lattices. In the presence of a nested Fermi surface, the bosons may develop a fascinating supersolid behavior characterized by a finite superfluid density as well as a spatial density wave order. Focusing on the triangular lattice geometry and combining a general Landau-Ginzburg-Wilson approach with microscopically derived mean-field theory, we find an exotic supersolid phase at a fermionic band-filling of $n_f=3/4$ with a Kagome-type crystalline order. We also address the case of anisotropic hopping amplitudes, and show that striped supersolid phases emerge on the square and triangular lattices. For weak interactions, the supersolid competes with phase separation. For strong intra- and inter-species interactions, with the total number of fermions and bosons corresponding to one particle per site, the bosons form an alternating Mott insulator ground state. Finally, for a mixture of ${}^{87}{\text{Rb}}^{40}\text{K}$ and ${}^{23}{\text{Na}}^6\text{Li}$, we show that supersolidity can be observed in the range of accessible temperatures in the square lattice geometry.

Moved technical details to appendices. Enlarged list of references. Corrected typos, new Figs.11 and 15. Final and published version

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• Zero-temperature phase diagram of Bose-Fermi gaseous mixtures in optical lattices
• Competing Superconducting States for Ultracold Atoms in Optical Lattices with Artificial Staggered Magnetic Field
• Inhomogeneous hard-core bosonic mixture with checkerboard supersolid phase: Quantum and thermal phase diagram
• Phases and collective modes of bosons in a triangular lattice at finite temperature: A cluster mean field study
• Spontaneous quantum Hall effect in an atomic spinor Bose-Fermi mixture
• Noise correlations of one-dimensional Bose mixtures in optical lattices
• On the Sign of Fermion-Mediated Interactions
• Spin-selective insulators in Bose-Fermi mixtures
• Insulator phases of Bose-Fermi mixtures induced by intraspecies next-neighbor interactions
• Supersolid in Bose-Bose-Fermi Mixtures subjected to a Square Lattice