Commensurate Supersolid of Three-Dimensional Lattice Bosons

TL;DR

This paper provides evidence for a three-dimensional lattice boson model exhibiting a stable supersolid phase at a commensurate filling factor of 1/2, without doping, using quantum Monte Carlo simulations.

Contribution

It demonstrates the existence of a commensurate supersolid in a 3D Bose-Hubbard model, challenging the conventional doping mechanism for supersolid formation.

Findings

Evidence of a checkerboard supersolid at 1/2 filling in 3D lattice bosons.

Supersolid stability at commensurate filling without doping.

Observation of unbound interstitial-vacancy pairs in the crystal.

Abstract

Using an unbiased quantum Monte Carlo method, we obtain convincing evidence of the existence of a checkerboard supersolid at a {\it commensurate} filling factor 1/2 (commensurate supersolid) in the soft-core Bose-Hubbard model with nearest-neighbor repulsions on a cubic lattice. In conventional cases, supersolids are realized at incommensurate filling factors by a doped-defect-condensation mechanism, where particles (holes) doped into a perfect crystal act as interstitials (vacancies) and delocalize in the crystal order. However, in the above model, a supersolid state is stabilized even at the commensurate filling factor 1/2 {\it without doping}. By performing grand canonical simulations, we obtain a ground-state phase diagram that suggests the existence of a supersolid at a commensurate filling. To obtain direct evidence of the commensurate supersolid, we next perform simulations in canonical ensembles at a particle density $\rho=1/2$ and exclude the possibility of phase separation. From the obtained snapshots, we discuss the microscopic structure and observe that interstitial-vacancy pairs are unbound in the crystal order.