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

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 Na-23, K-39, and K-41 atomic species, in which the binary mixtures of (Na-23, K-39) and (K-39, K-41) can form self-bound quantum droplets stabilized by quantum fluctuations. Two such droplets can bind together by the shared K-39 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 (Na-23, K-39) and (K-39, K-41) droplets. This structure exhibits both periodic density modulations from the droplet ordering and global phase coherence due to the shared K-39 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 alternative 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.