Helical superfluid in a frustrated honeycomb Bose-Hubbard model

TL;DR

This paper investigates a novel helical superfluid state in a frustrated honeycomb Bose-Hubbard model, revealing its unique properties, phase transitions, and potential experimental realizations.

Contribution

It introduces and analyzes a helical superfluid with nonzero momentum condensate, developing a phase diagram and a field theory consistent with microscopic models.

Findings

Identification of a helical superfluid with nonzero momentum condensate

Discovery of a smectic fluctuation regime stronger than in conventional superfluids

Observation of order-by-disorder leading to a crossover to an anisotropic XY superfluid

Abstract

We study a "helical" superfluid, a nonzero-momentum condensate in a frustrated bosonic model. At mean-field Bogoliubov level, such a novel state exhibits "smectic" fluctuation that are qualitatively stronger than that of a conventional superfluid. We develop a phase diagram and compute a variety of its physical properties, including the spectrum, structure factor, condensate depletion, momentum distribution, all of which are qualitatively distinct from that of a conventional superfluid. Interplay of fluctuations, interaction and lattice effects gives rise to the phenomenon of order-by-disorder, leading to a crossover from the smectic superfluid regime to the anisotropic XY superfluid phase. We complement the microscopic lattice analysis with a field theoretic description for such a helical superfluid, which we derive from microscopics and justify on general symmetry grounds, reassuringly finding full consistency. Possible experimental realizations are discussed.