Helical superfluid in a frustrated honeycomb Bose-Hubbard model

Tzu-Chi Hsieh^1*, Han Ma², Leo Radzihovsky¹

¹Department of Physics, University of Colorado Boulder, Boulder, Colorado, USA
²Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada

* Presenter:Tzu-Chi Hsieh, email:zihcisie@gmail.com

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.

Keywords: Bose-Einstein condensates, Frustrated magnetism, Bose-Hubbard model