86 research outputs found

    Spin-Peierls states of quantum antiferromagnets on the CaV4O9Ca V_4 O_9 lattice

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    We discuss the quantum paramagnetic phases of Heisenberg antiferromagnets on the 1/5-depleted square lattice found in CaV4O9Ca V_4 O_9. The possible phases of the quantum dimer model on this lattice are obtained by a mapping to a quantum-mechanical height model. In addition to the ``decoupled'' phases found earlier, we find a possible intermediate spin-Peierls phase with spontaneously-broken lattice symmetry. Experimental signatures of the different quantum paramagnetic phases are discussed.Comment: 9 pages; 2 eps figure

    Renormalization Group for Large N Strongly Commensurate Dirty Boson Model

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    The large N sigma model, in D<4 space-time dimensions, with disorder a function of d space dimensions, is analyzed via a renormalization group treatment. Critical exponents for average quantities are calculated, first to lowest order and then to all orders, in ϵ=D−2−d/2\epsilon=D-2 - d/2. In particular, it is found that νd=2\nu d =2. When D=d+1, this model is equivalent to a large N limit of the strongly commensurate dirty boson problem.Comment: 16 pages, 4 figures, to be published in PR

    Renormalization Group Approach to the Infrared Behavior of a Zero-Temperature Bose System

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    We exploit the renormalization-group approach to establish the {\em exact} infrared behavior of an interacting Bose system at zero temperature. The local-gauge symmetry in the broken-symmetry phase is implemented through the associated Ward identities, which reduce the number of independent running couplings to a single one. For this coupling the ϵ\epsilon-expansion can be controlled to all orders in ϵ\epsilon (=3−d=3-d). For spatial dimensions 1<d≤31 < d \leq 3 the Bogoliubov fixed point is unstable towards a different fixed point characterized by the divergence of the longitudinal correlation function. The Bogoliubov linear spectrum, however, is found to be independent from the critical behavior of this correlation function, being exactly constrained by Ward identities. The new fixed point properly gives a finite value of the coupling among transverse fluctuations, but due to virtual intermediate longitudinal fluctuations the effective coupling affecting the transverse correlation function flows to zero. As a result, no transverse anomalous dimension is present. This treatment allows us to recover known results for the quantum Bose gas in the context of a unifying framework and also to reveal the non-trivial skeleton structure of its perturbation theory.Comment: 21 page

    Terawatt, Joule-Class Pulsed THz Sources from Microchannel Targets

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    Production of terawatt, joule class THz radiation sources from microchannel targets driven with 100s of joule, picosecond lasers is reported. THz sources of this magnitude are useful for non-linear pumping of matter and for charged particle acceleration and manipulation. Microchannel targets demonstrate increased conversion efficiency compared to planar foil targets, with laser energy to THz energy conversion up to 0.9 percent.Comment: 9 pages, 2 figure

    The density dependence of the transition temperature in a homogenous Bose flui

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    Transition temperature data obtained as a function of particle density in the 4^4He-Vycor system are compared with recent theoretical calculations for 3D Bose condensed systems. In the low density dilute Bose gas regime we find, in agreement with theory, a positive shift in the transition temperature of the form ΔT/T0=γ(na3)1/3\Delta T/T_0 = \gamma(na^{3})^{1/3}. At higher densities a maximum is found in the ratio of Tc/T0T_c /T_0 for a value of the interaction parameter, na3^3, that is in agreement with path-integral Monte Carlo calculations.Comment: 4 pages, 3 figure

    Two-particle pairing and phase separation in a two-dimensional Bose-gas with one or two sorts of bosons

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    We present a phase diagram for a dilute two-dimensional Bose-gas on a lattice. For one sort of boson we consider a realistic case of the van der Waals interaction between particles with a strong hard-core repulsion UU and a van der Waals attractive tail VV. For V<2tV< 2 t , tt being a hopping amplitude, the phase diagram of the system contains regions of the usual one-particle Bose-Einstein condensation (BEC). However for V>2tV>2t we have total phase separation on a Mott-Hubbard Bose solid and a dilute Bose gas. For two sorts of structureless bosons described by the two band Hubbard model an s-wave pairing of the two bosons of different sort ≠0 \neq 0 is possible. The results we obtained should be important for different Bose systems, including submonolayers of 4^4He, excitons in semiconductors, Schwinger bosons in magnetic systems and holons in HTSC. In the HTSC case a possibility of two-holon pairing in the slave-bosons theories of superconductivity can restore a required charge 2e2e of a Cooper pair.Comment: 10 pages, 2 figure

    Interaction effects in non-Hermitian models of vortex physics

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    Vortex lines in superconductors in an external magnetic field slightly tilted from randomly-distributed parallel columnar defects can be modeled by a system of interacting bosons in a non-Hermitian vector potential and a random scalar potential. We develop a theory of the strongly-disordered non-Hermitian boson Hubbard model using the Hartree-Bogoliubov approximation and apply it to calculate the complex energy spectra, the vortex tilt angle and the tilt modulus of (1+1)-dimensional directed flux line systems. We construct the phase diagram associated with the flux-liquid to Bose-glass transition and find that, close to the phase boundary, the tilted flux liquid phase is characterized by a band of localized excitations, with two mobility edges in its low-energy spectrum.Comment: 19 pages, 19 figures, To appear in Phys. Rev.

    Rotating Shallow Water Dynamics: Extra Invariant and the Formation of Zonal Jets

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    We show that rotating shallow water dynamics possesses an approximate (adiabatic-type) positive quadratic invariant, which exists not only at mid-latitudes (where its analogue in the quasigeostrophic equation has been previously investigated), but near the equator as well (where the quasigeostrophic equation is inapplicable). Deriving the extra invariant, we find "small denominators" of two kinds: (1) due to the triad resonances (as in the case of the quasigeostrophic equation) and (2) due to the equatorial limit, when the Rossby radius of deformation becomes infinite. We show that the "small denominators" of both kinds can be canceled. The presence of the extra invariant can lead to the generation of zonal jets. We find that this tendency should be especially pronounced near the equator. Similar invariant occurs in magnetically confined fusion plasmas and can lead to the emergence of zonal flows.Comment: 29 pages, 4 figure
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