The superconducting transition temperatures of high-T C compounds based on copper, iron, ruthenium and certain organic molecules are discovered to be dependent on bond lengths, ionic valences, and Coulomb coupling between electronic bands in adjacent, spatially separated layers. 1 Optimal transition temperature, denoted as T C0 , is given by the universal expression k B T C0 = e 2  / ℓζ; ℓ is the spacing between interacting charges within the layers, ζ is the distance between interacting layers and  is a universal constant, equal to about twice the reduced electron Compton wavelength (suggesting that Compton scattering plays a role in pairing). Non-optimum compounds in which sample degradation is evident typically exhibit T C < T C0 . For the 31+ optimum compounds tested, the theoretical and experimental T C0 agree statistically to within  1.4 K. The elemental high T C building block comprises two adjacent and spatially separated charge layers; the factor e 2 / ζ arises from Coulomb forces between them. The theoretical charge structure representing a room-temperature superconductor is also presented.

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The flux-flow critical current as a function of transverse magnetic field for an oxygen-doped Al film perforated with a two-dimensional triangular lattice pattern of holes shows pronounced structure at harmonically related values of the applied magnetic field. Effects at thecharacteristic fields are interpreted in terms of the interaction between commensurate flux-line sublattices, one of which is strongly pinned to the holes by the vortex-hole coupling force and the other of which is located interstitially between the hole-lattice sites. A model is proposed for the vortex-hole coupling force which, in conjunction with a treatment of vortex-vortex interactions, qualitatively accounts for the observed temperature and field dependence of these harmonically related critical currents.

Transport anisotropies of p,/p, b =10 to 105 were measured for superconducting and nonsuperconducting Bi2+ Sr2-~CuO&+& crystals. In superconducting samples p,b increases linearly with temperature from just above T, =7 to 700 K. The implication of the p,b results is that classical electron-phonon scattering mechanisms are inadequate.The anisotropy and T, for various layered superconductor systems are compared. In all crystals studied p, is nonmetallic, varying as a power law T ', a=0.5-1.A characteristic feature of the high-T, layered superconductors is the extreme two dimensionality of their physical properties.Transport anisotropy studies are hence very significant for establishing the role of the coupling between Cu-0 planes on the mechanism of high-T, superconductivity.Previous measurements in Y-Ba-Cu-0 crystals suggested resistivity anisotropies of = 102 for samples with Tc 90 K, ' and =10 for 60-K samples.In Bi-Sr-Ca-Cu-0 crystals even larger anisotropies of =10 to 10 were measured, ' giving rise to twodimensional (2D) phase ffuctuations near the superconducting transition. 3 Similar behavior was recently reported for Tl-Ba-Ca-Cu-0 thin films. Presently, the mechanism of charge transport perpendicular to the Cu-0 planes is far from being clearly established, owing to the range of anisotropy values and the diff'erent types of tem-