Collective excitations of a Bose–Einstein condensate of hard-core bosons and their mediated interactions: from two-body bound states to mediated superfluidity

Abstract

The exchange of collective modes has been demonstrated to be a powerful tool for inducing superconductivity and superfluidity in various condensed matter and atomic systems. In this article, we study the mediated interactions of collective excitations in an ultracold gas of hard-core bosons. We show that the induced interaction supports two-body states with energies, symmetries, and a number of bound states strongly dependent on the properties of the hard-core boson gas. The ability to control the nature of the two-body bound states motivates the study of superfluid phases, which we address within the BKT theory. We demonstrate how the superfluid parameters and critical temperatures can be tuned in our system. Our findings may pave the way for future theoretical and experimental studies with ultracold gases and solid-state systems.

Lattice polaron in a Bose–Einstein condensate of hard-core bosons

“…In bilayers, moiré superlattices enable the realization of Hubbard models [80,81]. Very recently, the first Bose-Fermi-Hubbard model was realized in these systems [82]. Given the ability to tune Hubbard model parameters through the relative twist angle, we expect our study to draw attention towards realizing mediated superconductivity in these systems.…”

“…We start describing the gas of hard-core bosons. The derivation outlined in this subsection can be found in [81,82], however, to make our manuscript more pedagogical, we include here a detailed derivation. The Hamiltonian of the majority bosons is given by…”