Abstract
The successful emulation of the Hubbard model in optical lattices has stimulated extensive efforts to extend their scope to also capture more complex, incompletely understood scenarios of many-body physics. A promising approach is to consider higher bands, where the orbital degree of freedom gives rise to a structural diversity that is directly relevant, for example, for the physics of strongly correlated electronic matter. Here we report evidence for the formation of a superfluid in the P-band of a bipartite optical square lattice with S-orbits and P-orbits arranged in a chequerboard pattern. The observed momentum spectra feature cross-dimensional coherence with a lifetime of nearly 20 ms. Depending on the value of a small adjustable anisotropy of the lattice, our findings are explained either by real-valued striped superfluid order parameters with different orientations Px±Py, or by a complex-valued Px±i Py order parameter, which breaks time-reversal symmetry.
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Acknowledgements
This work was partially supported by DFG (He2334/10-1) and the Excellence Cluster ‘Frontiers in Quantum Photon Science’. We are grateful to C. Morais Smith and L-K. Lim for fruitful discussions.
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Wirth, G., Ölschläger, M. & Hemmerich, A. Evidence for orbital superfluidity in the P-band of a bipartite optical square lattice. Nature Phys 7, 147–153 (2011). https://doi.org/10.1038/nphys1857
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DOI: https://doi.org/10.1038/nphys1857
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