Nematic quantum liquid crystals of bosons in frustrated lattices

TL;DR

This paper predicts the emergence of nematic quantum liquid crystalline phases, including Wigner crystal, supersolid, and superfluid, in frustrated lattice models of bosons with flat energy bands, revealing novel anisotropic condensation phenomena.

Contribution

It introduces a new theoretical framework for understanding nematic phases of bosons in flat band frustrated lattices, including exact and mean-field analyses of these exotic states.

Findings

Wigner crystal phase established at low filling

Prediction of a nematic superfluid with anisotropic momentum distribution

Identification of supersolid phase at higher filling

Abstract

The problem of interacting bosons in frustrated lattices is an intricate one due to the absence of a unique minimum in the single-particle dispersion where macroscopic number of bosons can condense. Here we consider a family of tight-binding models with macroscopically degenerate lowest energy band, separated from other bands by a gap. We predict the formation of exotic states that spontaneously break rotational symmetry at relatively low filling. These states belong to three nematic phases: Wigner crystal, supersolid, and superfluid. The Wigner crystal phase is established exactly at low filling. Supersolid and superfluid phases, at larger filling, are obtained by making use of a projection onto the flat band, construction of an appropriate Wannier basis, and subsequent mean-field treatment. The nematic superfluid that we predict is uniform in real space but has an anisotropic momentum distribution, providing a novel scenario for Bose condensation with an additional nematic order. Our findings open up a promising direction of studying microscopic quantum liquid crystalline phases of bosons.