Abstract
We show that correlated pair tunneling drives a phase transition to a twisted superfluid with a complex order parameter. This unconventional superfluid phase spontaneously breaks the time-reversal symmetry and is characterized by a twisting of the complex phase angle between adjacent lattice sites. We discuss the entire phase diagram of the extended Bose—Hubbard model for a honeycomb optical lattice showing a multitude of quantum phases including twisted superfluids, pair superfluids, supersolids and twisted supersolids. Furthermore, we show that the nearest-neighbor interactions lead to a spontaneous breaking of the inversion symmetry of the lattice and give rise to dimerized density-wave insulators, where particles are delocalized on dimers. For two components, we find twisted superfluid phases with strong correlations between the species already for surprisingly small pair-tunneling amplitudes. Interestingly, this ground state shows an infinite degeneracy ranging continuously from a supersolid to a twisted superfluid.
Highlights
We show that correlated pair tunneling drives a phase transition to a twisted superfluid with a complex order parameter
We show that the nearestneighbor interactions lead to a spontaneous breaking of the inversion symmetry of the lattice and give rise to dimerized density-wave insulators, where particles are delocalized on dimers
We study the extended Bose—Hubbard model with two additional processes arising from the interaction of particles on adjacent sites known as nearest-neighboring interaction V and pair tunneling P
Summary
We show that correlated pair tunneling drives a phase transition to a twisted superfluid with a complex order parameter. A spontaneous time-reversal symmetry breaking associated with complex order parameters has been observed in the pseudo-gap phase of the high-temperature superconductor Bi-2212 with ARPES8, as well as in Sr2RuO4 using a muon spin relaxation measurement[10] and UPt3 via the polar Kerr effect[11,12,13]. In this respect, the twisted superfluidity interlinks many-body quantum gas systems with superconducting materials. The twisted superfluid is characterized by strong correlations between the two components and exhibits an infinite ground-state degeneracy
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