Incompressible excitonic superfluid of ultracold Bose atoms in an optical lattice: a new superfluid phase in the one-component Bose-Hubbard model

TL;DR

This paper predicts a novel incompressible excitonic superfluid phase in ultracold Bose atoms within optical lattices, characterized by spontaneous translation symmetry breaking, stable against fluctuations, and distinguishable from conventional superfluids.

Contribution

It introduces the incompressible excitonic superfluid (IESF) phase in the Bose-Hubbard model, with theoretical analysis of its stability, critical temperature, and experimental signatures.

Findings

Identification of IESF as a new stable superfluid phase

Critical temperature of IESF independent of interaction strength

IESF is incompressible, unlike conventional superfluids

Abstract

We predict that a new superfluid phase, the incompressible excitonic superfluid (IESF), in the phase diagram of ultracold Bose atoms in $d>1$ dimensional optical lattices, which is caused by the spontaneous breaking of the symmetry of translation of the lattice. Within mean field theory, the critical temperature of the phase transition from this IESF to the normal fluid (NF) is calculated and the triple-critical point of the three phases is determined. We also investigate both configuration and gauge field fluctuations and show the IESF state is stable against these fluctuations. We expect this IESF phase can be experimentally observed by loading cold Bose atoms into a two-dimensional lattice where the atom filling fraction deviates slightly from exact commensurations. The signatures distinguishing this IESF from the common atom superfluid (ASF) are that (i) the critical temperature of the IEST/NF transition is independent of interaction, unlike the ASF/NF transition; (ii) the IESF is incompressible while the ASF is compressible.