Twisted complex superfluids in optical lattices

1 April 2015

Photo: AG Sengstock

The time-reversal symmetry of the Schrödinger equation allows us to describe superfluid ground states with real wave functions in accordance with Feynman's no-node theorem. 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. Furthermore, we show that the nearest-neighbor interactions breaks the inversion symmetry of the lattice and gives rise to dimerized density-wave insulators, where particles are delocalized on dimers. For two components, we find twisted superfluid phases with an infinite degeneracy for surprisingly small pair-tunneling amplitudes.

Scientific Reports 5, 12912 (2015)