Quantum diatomic chain: a supersolid structure in three-component Bose mixture

TL;DR

This paper theoretically demonstrates a supersolid structure in a three-component Bose mixture, where quantum droplets form a stable chain with both density modulations and phase coherence, expanding the understanding of supersolidity.

Contribution

It introduces a new class of supersolids formed by mediated binding in a three-component Bose mixture, without relying on long-range interactions or engineered band structures.

Findings

Stable droplet dimers form via quantum fluctuations.

A linear chain of alternating droplets exhibits supersolidity.

Low-energy excitations include droplet vibrations and superfluid modes.

Abstract

The formation and properties of a supersolid structure in a three-component ultracold Bose gas mixture at T=0 are investigated theoretically. The system consists of 23Na, 39K, and 41K atomic species, in which the binary mixtures of (23Na,39K) and (39K,41K) can form self-bound quantum droplets stabilized by quantum fluctuations. Two such droplets can bind together by the shared 39K component, forming a stable "dimer" structure, which displays vibrational modes analogous to a classical diatomic molecule. A simple protocol is proposed to create a stable linear chain formed by periodic repetition of this basic building block, i.e. an alternating sequence of (23Na,39K) and (39K,41K) droplets. This structure exhibits both periodic density modulations from the droplet ordering and global phase coherence due to the shared 39K component, satisfying the criteria for supersolidity. This expands the class of known supersolids by adding a system where mediated binding, rather than intrinsic long-range interactions or engineered band-structures as in previously known supersolids, is the key organizing principle, thereby offering new directions for both theory and experiment. The low-energy excitation spectrum, probed by density perturbations, identifies modes corresponding to droplet vibrations close to the ones expected from a classical diatomic chain, coexisting with low-energy superfluid (Goldstone-type) modes.