Topological phase separation in 2D quantum lattice Bose-Hubbard system away from half-filling

TL;DR

This paper predicts that doping a 2D hard-core boson lattice system can lead to topological phase separation with inhomogeneous charge and superfluid regions, influenced by lattice parameters and quantum effects.

Contribution

It introduces a theoretical framework for topological phase separation in doped 2D bosonic systems, highlighting the role of lattice interactions and quantum effects in inhomogeneous phases.

Findings

Topological inhomogeneity can form in doped 2D bosonic systems.

Order parameter symmetry depends on transfer integrals.

Inhomogeneous phases show signatures of multiple symmetries.

Abstract

We suppose that the doping of the 2D hard-core boson system away from half-filling may result in the formation of multi-center topological inhomogeneity (defect) such as charge order (CO) bubble domain(s) with Bose superfluid (BS) and extra bosons both localized in domain wall(s), or a {\it topological} CO+BS {\it phase separation}, rather than an uniform mixed CO+BS supersolid phase. Starting from the classical model we predict the properties of the respective quantum system. The long-wavelength behavior of the system is believed to remind that of granular superconductors, CDW materials, Wigner crystals, and multi-skyrmion system akin in a quantum Hall ferromagnetic state of a 2D electron gas. To elucidate the role played by quantum effects and that of the lattice discreteness we have addressed the simplest nanoscopic counterpart of the bubble domain in a checkerboard CO phase of 2D hc-BH square lattice. It is shown that the relative magnitude and symmetry of multi-component order parameter are mainly determined by the sign of the $nn$ and $nnn$ transfer integrals. In general, the topologically inhomogeneous phase of the hc-BH system away from the half-filling can exhibit the signatures both of $s,d$, and $p$ symmetry of the off-diagonal order.