Competing quantum phases of hard-core boson with tilted dipole-dipole interaction

TL;DR

This paper investigates the quantum phases of hard-core bosons with tilted dipole-dipole interactions on a square lattice, identifying competing phases and potential supersolid states relevant for ultracold atom experiments.

Contribution

It introduces a combined numerical and analytical study of dipolar bosons with tilted polarization, revealing phase boundaries and supersolid phases not previously characterized.

Findings

Identification of competing ordered phases with different unit cell sizes.

First-order phase transition between these phases.

Potential realization of effective triangular lattice in experiments.

Abstract

Different quantum phases of hard-core boson induced by dipole-dipole interaction with varying angles of polarization are discussed in this work. We consider the two most influential leading terms with anisotropy due to the tilted polarization of the on-site boson in the square lattice. To ensure the concreteness of this truncation, we compare our phase diagrams, obtained numerically from cluster mean-field theory (CMFT) and infinite projected entangled-pair state (iPEPS), with that of the long-range interacting model from quantum Monte Carlo. Next, we focus on the case where the azimuthal angle is fixed to $\phi = \pi/4$. Using the mean-field analysis where the quantum spin operators are replaced by $c$-numbers, we aim to search for the underlying phases, especially the supersolid. Our results show a competing scenario mainly between two ordered phases with different sizes of unit cell, where first-order transition takes place in between them. With the help of CMFT and variational iPEPS, the phase boundaries predicted by the mean-field theory are determined more precisely. Our discoveries elucidate the possible underlying supersolid phases which might be seen in the ultracold experiments with strongly dipolar atoms. Moreover, our results indicate that an effective triangular optical lattice can be realized by fine tuning the polarization of dipoles in a square lattice.