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We study the effects of pressure on the electron-phonon interaction in MgB_2 using density-functional-based methods. Our results show that the superconductivity in MgB_2 vanishes by 100 GPa, and then reappears at higher pressures. In particular, we find a superconducting transition temperature T_c \~ 2 K for mu*=0.1 at a pressure of 137 GPa., 4 pages, 6 figures; one figure and discussion on phonon softening added

The transport properties of superconductor/weak ferromagnet Nb/Pd86Ni14 sputtered bilayers have been studied. The critical thickness needed for superconductivity to develop is determined from the dependence of the transition temperature T-c on d(Nb). (c) 2005 Elsevier Ltd. All rights reserved.

The influence of vacancies in the C sublattice of MgCNi3, on its structural, electronic, and magnetic properties are studied by means of the density-functional-based Korringa-Kohn-Rostoker Green's function method formulated in the atomic sphere approximation. Disorder is taken into account by means of coherent-potential approximation. Characterizations representing the change in the lattice properties include the variation in the equilibrium lattice constants, bulk modulus, and pressure derivative of the bulk modulus, and those of the electronic structure include the changes in the total, partial, and k-resolved density of states. The incipient magnetic properties are studied by means of the fixed-spin moment method of alloy theory, together in conjunction with the phenomenological Ginzburg-Landau equation for magnetic phase transition. The first-principles calculations reveal that due to the breaking of the C-Ni bonds, some of the Ni 3d states, which were lowered in energy due to strong hybridization, are transferred back to higher energies thereby increasing the itinerant character in the material. The Bloch spectral densities evaluated at the high symmetry points, however, reveal that the charge redistribution is not uniform over the cubic Brillouin zone, as new states are seen to be created at the Gamma point, while a shift in the states on the energy scale are seen at other high symmetry points.

We report on an ultra-high vacuum (UHV) compatible method for fabricating devices of sub-micrometer size by virtue of a non-organic evaporation mask of high thermal and mechanical stability. As an application we describe the superconducting properties of mesoscopic superconductor=normal-metal and superconductor=ferromagnet=superconductor hybrid structures. In particular, we report on the observation of the DC-Josephson e9ect in Nb=Cu=Co=Cu=Nbstructures prepared in UHV. The Josephson coupling between the two superconductors through the very thin (5 nm) magnetic and metallic weak link is con;rmed by the magnetic ;eld dependence of the critical current Ic, which displays a Fraunhofer-like interference pattern.

A comparative study has been made of iodine-intercalated Bi2Sr2Ca1Cu2Ox single crystal and 1 atm O2 annealed Bi2Sr2Ca1Cu1Ox single crystal using an AC susceptibility measurement, X-ray photoemission (XPS) and angle-resolved ultraviolet photoemission spectroscopy (ARUPS). The AC susceptibility measurement indicates that O2 doped samples studied have a T(c) of 84 K, whereas T(c) of the iodine-doped samples studied are 80 K. XPS Cu 2p core-level data establish that the hole concentration in the CuO2 planes is essentially the same for these two kinds of samples. ARUPS measurements show that the electronic structure of the normal states near the Fermi level has been strongly affected by iodine intercalation. We conclude that the dominant effect of iodine doping is to alter the interlayer coupling.