Surface state and normal layer effects

In addition to the conducting CuO{sub 2} (S) layers, most high-T{sub c} superconductors also contain other conducting (N) layers, which are only superconducting due to the proximity effect. The combination of S and N layers can give rise to complicated electronic densities of states, leading to quasilinear penetration depth and NMR relaxation rate behavior at low temperatures. Surface states can also complicate the analysis of tunneling and, photoemission measurements. Moreover, geometrical considerations and in homogeneously trapped flux axe possible explanations of the paramagnetic Meissner effect and of corner and ring SQUID experiments. Hence, all of the above experiments could be consistent with isotropic s-wave superconductivity within the S layers

Theory of Tunneling for Rough Junctions

A formally exact expression for the tunneling current, for its separation into specular and diffuse components, and for its directionality, is given for a thick tunnel junction with rough interfaces in terms of the properties of appropriately defined scattering amplitudes. An approximate evaluation yields the relative magnitudes of the specular and diffuse components, and the angular dependence of the diffuse component, in terms of certain statistical properties of the junction interfaces.Comment: 4 page

Orthorhombicity mixing of s- and d- gap components in YBa2Cu3O7YBa_2Cu_3O_7 without involving the chains

Momentum decoupling develops when forward scattering dominates the pairing interaction and implies tendency for decorrelation between the physical behavior in the various regions of the Fermi surface. In this regime it is possible to obtain anisotropic s- or d-wave superconductivity even with isotropic pairing scattering. We show that in the momentum decoupling regime the distortion of the $CuO_2$ planes is enough to explain the experimental reports for s- mixing in the dominantly d-wave gap of $YBa_2Cu_3O_7$. In the case of spin fluctuations mediated pairing instead, a large part of the condensate must be located in the chains in order to understand the experiments.Comment: LATEX file and 3 Postscript figure

Structure of Magnetic Fields in High Temperature Superconductors with Columnar Defects

Superconductivity is expected to invade our daily life shortly. Technology involving the application of superconductivity will soon be found in different instruments, devices and machinery using a new family of high-temperature superconductors (HTS) where the critical temperature below which the material becomes superconductor has been raised to around half of room temperature. An essential issue that needs to accompany the spread of use of superconductivity is the development of NDE tools that can be used for such new technology.</p

Dependence of the Josephson coupling of unconventional superconductors on the properties of the tunneling barrier

The Josephson coupling between a conventional and an unconventional superconductor is investigated as a function of the properties of the tunneling barrier. A simple model is adopted for the tunneling probability and it is shown that its variation dramatically affects the I{sub c}R{sub n} product of an s-d, as opposed to an s-s junction. Based on these conclusions, experiments are proposed to probe the symmetry of the order parameter in high temperature superconductors

Surface state and normal layer effects in high T{sub c} superconductors

In addition to the conducting CuO{sub 2} (S) layers, most high-{Tc}, superconductors also contain other conducting (N) layers, which are only superconducting due to the proximity effect. The combination of S and N layers can give rise to complicated electronic densities of states, leading to quasilinear penetration depth and NMR relaxation rate behavior at low temperatures. Surface states can also complicate the analysis of tunneling and photoemission measurements. Moreover, geometrical considerations and inhomogeneously trapped flux are possible explanations of the paramagnetic Meissner effect and of corner and ring SQUID experiments. Hence, all of the above experiments could be consistent with isotropic s-wave superconductive within the S layers

Comment on {open_quotes}superfluid anisotropy in YBCO: Evidence for pair tunneling superconductivity{close_quotes}

Recently, Xiang and Wheatley extended our proximity coupling SN model of the (S) CuO{sub 2} plane and (N) CuO chain layers in YBCO compounds, using the single particle bands {epsilon}{sup 0}{sub 1k} = -t(cos k{sub a} + cos k{sub b}) - {mu}{sub 1} and {epsilon}{sup 0}{sub 2k} = -t{sub 2y}cos k{sub b} - {mu}{sub 2}, respectively. Although we showed that it was possible to fit the penetration depth {lambda}{sub ab}(T) in twinned YBCO with either s- or d-wave pairing and both bands free-particle-like, they claimed that: (1) It is impossible to fit the quasi-linear {lambda}{sub a}(T) in untwinned YBCO without order parameter line nodes, such as for d{sub x2-y2} pairing. (2) Even d-wave SN fits to the {lambda}{sub a,b,c} data are inferior to those obtained from a model of d-wave interlayer pair tunneling (DIPT). We remark that their claim is false, and ignores other data favoring proximity coupling

TRANSITION-TEMPERATURES OF SUPERCONDUCTOR-FERROMAGNET SUPERLATTICES

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