103 research outputs found

    Theory of Coherent cc-Axis Josephson Tunneling between Layered Superconductors

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    We calculate exactly the Josephson current for cc-axis coherent tunneling between two layered superconductors, each with internal coherent tight-binding intra- and interlayer quasiparticle dispersions. Our results also apply when one or both of the superconductors is a bulk material, and include the usually neglected effects of surface states. For weak tunneling, our results reduce to our previous results derived using the tunneling Hamiltonian. Our results are also correct for strong tunneling. However, the cc-axis tunneling results of Tanaka and Kashiwaya are shown to be incorrect in any limit. In addition, we consider the cc-axis coherent critical current between two identical layered superconductors twisted an angle ϕ0\phi_0 about the cc-axis with respect to each other. Regardless of the order parameter symmetry, our coherent tunneling results using a tight-binding intralayer quasiparticle dispersion are inconsistent with the recent cc-axis twist bicrystal Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta} twist junction experiments of Li {\it et al.}Comment: 11 pages, 13 figures, submitted to Physical Review

    Comment on "c-axis Josephson tunneling in Dx2y2D_{x^2-y^2}-wave superconductors''

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    This comment points out that the recent paper by Maki and Haas [Phys. Rev. B {\bf 67}, 020510 (2003)] is completely wrong.Comment: 1 page, submittted to Phys. Rev.

    Gaussian Tunneling Model of c-Axis Twist Josephson Junctions

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    We calculate the critical current density JcJJ^J_c for c-axis Josephson tunneling between identical high temperature superconductors twisted an angle ϕ0\phi_0 about the c-axis. We model the tunneling matrix element squared as a Gaussian in the change of wavevector q parallel to the junction, <t(q)2>exp(q2a2/2π2σ2)<|t({\bf q})|^2>\propto\exp(-{\bf q}^2a^2/2\pi^2\sigma^2). The JcJ(ϕ0)/JcJ(0)J^J_c(\phi_0)/J^J_c(0) obtained for the s- and extended-s-wave order parameters (OP's) are consistent with the Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta} data of Li {\it et al.}, but only for strongly incoherent tunneling, σ20.25\sigma^2\ge0.25. A dx2y2d_{x^2-y^2}-wave OP is always inconsistent with the data. In addition, we show that the apparent conventional sum rule violation observed by Basov et al. might be understandable in terms of incoherent c-axis tunneling, provided that the OP is not dx2y2d_{x^2-y^2}-wave.Comment: 6 pages, 6 figure

    Heisenberg Dimer Single Molecule Magnets in a Strong Magnetic Field

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    We calculate the static and dynamic properties of single crystal, single molecule magnets consisting of equal spin S=1/2S=1/2 or 5/2 dimers. The spins in each dimer interact with each other via the Heisenberg exchange interaction and with the magnetic induction B{\bf B} via the Zeeman interaction, and interdimer interactions are negligible. For antiferromagnetic couplings, the static magnetization and specific heat exhibit interesting low temperature TT and strong B{\bf B} quantum effects. We calculate the frequency spectrum of the Fourier transform of the real part of the time autocorrelation function C11(t){\cal C}_{11}(t) for arbitrary T,BT, {\bf B}, and compare our results with those obtained for classical spins. We also calculate the inelastic neutron magnetic dynamical structure factor S(q,ω)S({\bf q},\omega) at arbitrary T,BT, {\bf B}.Comment: 11 pages, 14 figures, submitted to Phys. Rev.

    Properties of the Ideal Ginzburg-Landau Vortex Lattice

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    The magnetization curves M(H) for ideal type-II superconductors and the maximum, minimum, and saddle point magnetic fields of the vortex lattice are calculated from Ginzburg-Landau theory for the entire ranges of applied magnetic fields Hc1 <= H < Hc2 or inductions 0 <= B < Hc2 and Ginzburg-Landau parameters sqrt(1/2) <= kappa <= 1000. Results for the triangular and square flux-line lattices are compared with the results of the circular cell approximation. The exact magnetic field B(x,y) and magnetization M(H, kappa) are compared with often used approximate expressions, some of which deviate considerably or have limited validity. Useful limiting expressions and analytical interpolation formulas are presented.Comment: 11 pages, 8 figure

    Non-ohmic critical fluctuation conductivity of layered superconductors in magnetic field

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    Thermal fluctuation conductivity for a layered superconductor in perpendicular magnetic field is treated in the frame of the self-consistent Hartree approximation for an arbitrarily strong in-plane electric field. The simultaneous application of the two fields results in a slightly stronger suppression of the superconducting fluctuations, compared to the case when the fields are applied individually.Comment: 4 pages, 1 figure, to be published in Phys. Rev.

    Exact Mesonic Vacua From Matrix Models

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    We investigate in detail the structure of mesonic vacua of N=1 U(Nc) supersymmetric gauge theory with Nf flavors from the matrix model. We show that the Witten index from the matrix model calculation agrees with a result from field theoretical analysis. We also discuss the relationship between a diagrammatic summation and direct matrix integration with insertion of a variable changing delta function. Using this formalism, we obtain the quantum moduli space and evidence of the Seiberg duality from the matrix models.Comment: 14 pages, 1 figure, typos corrected and note on the quamtum moduli space adde