1,173 research outputs found

    Nernst effect and diamagnetic response in a stripe model of superconducting cuprates

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    We examine the possibility that the experimentally observed enhancement of superconducting (SC) fluctuations above the SC transition temperature in the underdoped cuprates is caused by stripes -- an intrinsic electronic inhomogeneity, common to hole-doped cuprates. By evaluating the strengths of the diamagnetic response and the Nernst effect within the striped SC model, we find results that are qualitatively consistent with the experimental observations. We make a prediction for anisotropic thermopower in detwinned samples that can be used to further test the proposed scenario.Comment: 5 pages, 3 figures; final version published in Europhysics Letter

    Effects of doping on thermally excited quasiparticles in the high-TcT_c superconducting state

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    The physical properties of low energy superconducting quasiparticles in high- TcT_c superconductors are examined using magnetic penetration depth and specific heat experimental data. We find that the low energy density of states of quasiparticles of La2x_{2-x}Srx_xCuO4_4 scales with (xxc)/Tc(x-x_c)/T_c to the leading order approximation, where xcx_c is the critical doping concentration below which Tc=0T_c=0. The linear temperature term of the superfluid density is renormalized by quasiparticle interactions and the renormalization factor times the Fermi velocity is found to be doping independent.Comment: 3 pages, 3 figures, minor change to the content, fig1 is reploted, to appear in Phys Rev

    The Critical Hopping Parameter in O(a) improved Lattice QCD

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    We calculate the critical value of the hopping parameter, κc\kappa_c, in O(a) improved Lattice QCD, to two loops in perturbation theory. We employ the Sheikholeslami-Wohlert (clover) improved action for Wilson fermions. The quantity which we study is a typical case of a vacuum expectation value resulting in an additive renormalization; as such, it is characterized by a power (linear) divergence in the lattice spacing, and its calculation lies at the limits of applicability of perturbation theory. The dependence of our results on the number of colors NN, the number of fermionic flavors NfN_f, and the clover parameter cSWc_{SW}, is shown explicitly. We compare our results to non perturbative evaluations of κc\kappa_c coming from Monte Carlo simulations.Comment: 11 pages, 2 EPS figures. The only change with respect to the original version is inclusion of the standard formulae for the gauge fixing and ghost parts of the action. Accepted for publication in Physical Review

    Low Temperature Superfluid Response of High-Tc Superconductors

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    We have reviewed our theoretical and experimental results of the low temperature superfluid response function of high temperature superconductors (HTSC). In clean high-Tc materials the in-plane superfluid density rho_s^{ab} varies linearly with temperature. The slope of this linear T term is found to scale approximately with 1/Tc which, according to the weak coupling BCS theory for a d-wave superconductor, implies that the gap amplitude scales approximately with Tc. A T^5 behavior of the out-of-plane superfluid density rho_s^c for clean tetragonal HTSC was predicted and observed experimentally in the single layer Hg-compound HgBa_2CuO_{4+delta}. In other tetragonal high-Tc compounds with relatively high anisotropy, such as Hg_2Ba_2Ca_2Cu_3O_{8+delta}, rho_s^c varies as T^2 due to disorder effects. In optimally doped YBa_2Cu_3O_{7-delta}, rho_s^c varies linearly with temperature at low temperatures, but in underdoped YBa_2Cu_3O_{7-delta}, rho_s^c varies as T^2 at low temperatures; these results are consistent with our theoretical calculations.Comment: 26 pages, 8 figure

    Universal optimal hole-doping concentration in single-layer high-temperature cuprate superconductors

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    We argue that in cuprate physics there are two types, hole content per CuO2_2 plane (PplP_{pl}) and the corresponding hole content per unit volume (P3DP_{3D}), of hole-doping concentrations for addressing physical properties that are two-dimensional (2D) and three-dimensional (3D) in nature, respectively. We find that superconducting transition temperature (TcT_c) varies systematically with P3DP_{3D} as a superconducting \textquotedblleft domedome\textquotedblright with a universal optimal hole-doping concentration P3Dopt.P_{3D}^{opt.} = 1.6 ×\times 1021^{21} cm3^{-3} for single-layer high temperature superconductors. We suggest that P3Dopt.P_{3D}^{opt.} determines the upper bound of the electronic energy of underdoped single-layer high-TcT_c cuprates.Comment: 8 pages, 4 figures; added references ;accepted for the publication in Supercond. Sci. Technol ; Ref. 13 is revise

    Penetration Depth Measurements in MgB_2: Evidence for Unconventional Superconductivity

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    We have measured the magnetic penetration depth of the recently discovered binary superconductor MgB_2 using muon spin rotation and low field acac-susceptibility. From the damping of the muon precession signal we find the penetration depth at zero temperature is about 85nm. The low temperature penetration depth shows a quadratic temperature dependence, indicating the presence of nodes in the superconducting energy gap.Comment: 4 pages 3 figure

    Lattice effects in the La2x_{\rm 2-x}Srx_{\rm x}CuO4_{\rm 4} compounds

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    Systematic Raman studies on several cuprates (YBa2_{\rm 2}Cu3_{\rm 3}Ox_{\rm x}, YBa2_{\rm 2}Cu4_{\rm 4}O8_{\rm 8} or Bi2_{\rm 2}Sr2_{\rm 2}CaCu2_{\rm 2}O8_{\rm 8}) have shown that at optimal doping the compounds are at the edge of lattice instability; once this level is exceeded, by means of doping or applying external hydrostatic pressure, the changes in the transition temperature are accompanied by spectral modifications. There are strong indications that the reduction in Tc_{\rm c} is correlated with a separation into nanoscale phases, which involve the oxygen atoms of the CuO2_{\rm 2} planes. In this work, modifications with doping in the Raman spectra of the La2x_{\rm 2-x}Srx_{\rm x}CuO4_{\rm 4} compound are presented, which show that spin or charge ordering is coupled with lattice distortions in the whole doping region.Comment: 6 pages, 6 figure