Anomalous Behavior of Spin Systems with Dipolar Interactions

ArticleinPhysical Review Letters 109(2):025303 · July 2012with18 Reads
DOI: 10.1103/PhysRevLett.109.025303 · Source: PubMed
We study the properties of spin systems realized by cold polar molecules interacting via dipole-dipole interactions in two dimensions. Using a spin wave theory, that allows for the full treatment of the characteristic long-distance tail of the dipolar interaction, we find several anomalous features in the ground state correlations and the spin wave excitation spectrum, which are absent in their counterparts with short-range interaction. The most striking consequence is the existence of true long-range order at finite temperature for a two-dimensional phase with a broken U(1) symmetry.
    • "Here, σ ± = σ x ± iσ y . Such long-ranged spin Hamiltonians have been predicted to display anomalous properties as compared to their short-range counterparts [38, 39], making them attractive from the point of view of quantum simulation, and have been the subject of experimental studies using ultracold polar molecules pinned in optical lattices [40] or dipolar Bose–Einstein condensates [41]. "
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  • [Show abstract] [Hide abstract] ABSTRACT: We use a quantum Monte Carlo method to investigate various classes of 2D spin models with long-range interactions at low temperatures. In particular, we study a dipolar XXZ model with U(1) symmetry that appears as a hard-core boson limit of an extended Hubbard model describing polarized dipolar atoms or molecules in an optical lattice. Tunneling, in such a model, is short-range, whereas density-density couplings decay with distance following a cubic power law. We investigate also an XXZ model with long-range couplings of all three spin components - such a model describes a system of ultracold ions in a lattice of microtraps. We describe an approximate phase diagram for such systems at zero and at ?nite temperature, and compare their properties. In particular, we compare the extent of crystalline, super?uid, and supersolid phases. Our predictions apply directly to current experiments with mesoscopic numbers of polar molecules and trapped ions.
    Full-text · Article · Jun 2012
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