Phase diagram of soft-core bosons in two dimensions

Abstract

The low temperature phase diagram of Bose soft disks in two dimensions is studied by numerical simulations. It is shown that a supersolid cluster phase exists, within a range of the model parameters, analogous to that recently observed for a system of aligned dipoles interacting via a softened potential at short distance. These findings indicate that a long-range tail of the interaction is unneeded to obtain such a phase, and that the soft-core repulsive interaction is the minimal model for supersolidity

Excitation Spectrum of a Supersolid

“…The structural properties of the cluster crystal [8], with particles hopping between adjacent lattice sites, suggest an analogy with the Bose-Hubbard model which is clearly born by the spectral properties of both systems. While in continuous space the lattice is self-assembled, and thus features vibrational modes that are obviously absent in the BHM, the lower branch of the supersolid phase shows noteworthy similarities with the acoustic excitation present in the superfluid phase of the BHM.…”

“…This suggests that the incipient crystallization takes place with a lattice parameter larger than the mean interparticle distance. Indeed, upon increasing µ, the superfluid undergoes a first order phase transition into a triangular cluster (super)solid with a lattice spacing d somewhat larger than a [8]. The spectrum of the cluster crystal is also standard (we have studied longitudinal excitations only).…”

“…We take the soft-disk (SD) potential as representative [8] of the class of interactions described above, which support the phases of interest here.…”

“…Computer simulations have yielded evidence of a supersolid phase in a twodimensional system of spinless bosons in continuous space (i.e., not on a lattice), interacting through a specific class of soft-core repulsive potentials [7,8]. At low temperature and high density, despite the repulsive character of the interaction, particles pile up in clusters, in turn forming a periodic array, to which we refer as "cluster crystal" [9]: this is a lattice with a basis of K particles of the same kind and null basis vector.…”

Stable Dilute Supersolid of Two-Dimensional Dipolar Bosons

“…It is still under debate as to what extent experimental results in solid helium prove the existence of this conceptually important phase [21]. On the other hand, supersolidity is rather well understood theoretically for soft-core two-body potentials [20,[22][23][24][25][26], which can be realized, for example, in Rydberg-dressed atomic gases. However, such supersolids require a dense regime with at least several particles within the interaction range, which can be difficult to achieve.…”