Twisted complex superfluids in optical lattices

TL;DR

This paper explores how correlated pair tunneling induces a novel twisted superfluid phase with complex order parameters in optical lattices, revealing rich phase diagrams and symmetry-breaking phenomena.

Contribution

It introduces the concept of twisted superfluids driven by pair tunneling in the extended Bose-Hubbard model, including the analysis of phase diagrams and symmetry-breaking effects.

Findings

Identification of twisted superfluid phases with complex order parameters

Discovery of dimerized density-wave insulators due to inversion symmetry breaking

Observation of infinite degeneracy between supersolid and twisted superfluid states

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.