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Register a new userQuasiequilibrium supersolid phase of a two-dimensional dipolar crystal
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We have studied the possible existence of a supersolid phase of a two-dimensional dipolar crystal using quantum Monte Carlo methods at zero temperature. Our results show that the commensurate solid is not a supersolid in the thermodynamic limit. The presence of vacancies or interstitials turns the solid into a supersolid phase even when a tiny fraction of them are present in a macroscopic system. The effective interaction between vacancies is repulsive making a quasiequilibrium dipolar supersolid possible.
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The competition between tunneling and interactions in bosonic lattice models generates a whole variety of different quantum phases. While, in the presence of a single species interacting via on-site interaction, the phase diagram presents only superfluid or Mott insulating phases, for long-range interactions or multiple species, exotic phases such as supersolid (SS) or pair-superfluid (PSF) appear. In this work, we show for the first time that the co-existence of effective multiple species and long-range interactions leads to the formation of a novel pair-supersolid (PSS) phase, namely a supersolid of composites. We propose a possible implementation with dipolar bosons in a bilayer two-dimensional optical lattice.
Supersolid phases as a result of a coexistence of superfluid and density ordered checkerboard phases are predicted to appear in ultracold Fermi molecules confined in a bilayer array of two-dimensional square optical lattices. We demonstrate the existence of these phases within the inhomogeneous mean-field approach. In particular, we show that tuning the interlayer separation distance at a fixed value of the chemical potential produces different fractions of superfluid, density ordered, and supersolid phases.
We examine the superfluid and collapse instabilities of a quasi two-dimensional gas of dipolar fermions aligned by an orientable external field. It is shown that the interplay between the anisotropy of the dipolar interaction, the geometry of the system, and the p-wave symmetry of the superfluid order parameter means that the effective interaction for pairing can be made very large without the system collapsing. This leads to a broad region in the phase diagram where the system forms a stable superfluid. Analyzing the superfluid transition at finite temperatures, we calculate the Berezinskii--Kosterlitz--Thouless temperature as a function of the dipole angle.
We use a simple model to describe the nonlinear dynamics of a dense two dimensional dipolar exciton gas. The model predicts an initial fast expansion due to dipole-dipole pressure, followed by a much slower diffusion. The model is in very good agreement with recent experimental results. We show that the dipole pressure induced expansion strongly constrains the time available for achieving and observing Bose-Einstein quantum statistical effects, indicating a need for spatial exciton traps. We also suggest that nonlinear ballistic exciton transport due to the strong internal dipole pressure is readily achievable.
Distintictive features of supersolids show up in their rotational properties. We calculate the moment of inertia of a harmonically trapped dipolar Bose-Einstein condensed gas as a function of the tunable scattering length parameter, providing the transition from the (fully) superfluid to the supersolid phase and eventually to an incoherent crystal of self-bound droplets. The transition from the superfluid to the supersolid phase is characterized by a jump in the moment on inertia, revealing its first order nature. In the case of elongated trapping in the plane of rotation we show that the the moment of inertia determines the value of the frequency of the scissors mode, which is significantly affected by the reduction of superfluidity in the supersolid phase. The case of isotropic trapping is instead well suited to study the formation of quantized vortices, which are shown to be characterized, in the supersolid phase, by a sizeable deformed core, caused by the presence of the sorrounding density peaks.
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