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Magnetoconductance (MC) measurements have been performed on a 2140 A thick tungsten carbide film at temperatures very close to the superconducting transition temperature Tc of the film. The data are dominated by superconducting fluctuations. A novel three-dimensional phenomenological model is proposed to explain the MC data, yielding good fits. The Larkin beta factor, βLarkin, appeared as a fitting parameter. An expression proposed by Larkin for βLarkin failed badly for temperatures extremely close to Tc. But at intermediate and high temperatures compared to Tc, Larkin's expression gave very good agreement in fits to the MC data. At temperatures very close to Tc, a crossover from three dimensions to two dimensions was observed in the behaviour of the MC of the film.

The transition temperature T c and upper critical field H c2 of sputtered Fe/Nb trilayers and multilayers have been determined by measurement of electrical resistivity. For a fixed Fe layer thickness, T c decreases with decreasing Nb thickness up to a critical thickness d Nb crit ≈ 34 nm below which superconductivity vanishes. When the superconducting layers are thin ( d Nb 140 nm ) and decoupled by pair breaking in the ferromagnetic layers, the parallel critical field exhibits nonlinear temperature dependence, revealing a change in the superconducting dimensionality. The strong decrease of T c with decreasing Nb thickness as well as the temperature dependence of H c2 can be well described by theoretical model.

Superconducting YBa2Cu3O7−x films having smooth surfaces were successfully synthesized by a microwave plasma‐enhanced pulsed laser deposition (PEPLD) process. Particulates that frequently occurred in filmsgrown by the conventional PLD process were effectively eliminated. The films were epitaxial‐like. The c‐axis was perpendicular to the films’ surface, the a and b axes were aligned in the films’ plane, and the onset and zero of the transition temperature were at T c =90 K and T c0=86 K, respectively. Optical emission spectroscopy indicated that the presence of oxygen plasma not only reexcited the laser‐induced species via the collision process, but also produced abundant atomic oxygen in PEPLD process. The surface reaction kinetics for the formation of the thin‐film process was thus greatly enhanced, which substantially improved the thin‐film quality.

Electron tunneling measurements on ultrathin quench-condensed films near the superconductor-to-insulator (SI) transition reveal that the superconducting state degrades with increasing normal state sheet resistance, R□, in a manner that depends strongly on film morphology. In homogeneously disordered films, the superconducting energy gap Δo decreases continuously and appears to go to zero at the SI transition. In granular films the transport properties degrade while Δo remains constant. Measurements in the normal state reveal disorder enhanced e- -e- interaction corrections to the density of states. These effects are strong and depend on morphology in a manner that is consistent with their playing an important role in driving the SI transition.

We have measured the tunneling density of states in ultrathin high-sheet-resistance, 16 {Omega}{lt}{ital R}{sub {ital N}}{lt}17 k{Omega}, granular Pb films in perpendicular magnetic fields, {ital H}. At the lowest {ital R}{sub {ital N}}, states appear within the superconducting energy gap at low fields ({ital H}{lt}0.1 T) indicating the presence of vortex cores. At the highest {ital R}{sub {ital N}}, no states appear in the gap in fields as high as 2 T indicating that the field-induced vortices do not have cores. A simple model implies that the average Josephson coupling energy between the grains of the film is comparable to the condensation energy of a single grain at the {ital R}{sub {ital N}} separating these two regimes.

We have measured the perpendicular upper critical field, ${\mathit{H}}_{\mathit{c}2}$(T), in ultrathin granular Pb films with normal-state sheet resistances, ${\mathit{R}}_{\mathit{N}}$, that range from 10 \ensuremath{\Omega} to 11 k\ensuremath{\Omega}. The films with the highest ${\mathit{R}}_{\mathit{N}}$ are near the threshold for the superconductor-to-insulator (S-I) transition. We compare our results to calculations for granular superconductors and obtain values for the grain size and coherence length characteristic of a single grain. In addition, we present a measurement of the ratio of the intergrain Josephson-coupling energy to the single-grain condensation energy near the S-I transition in these films. The small value of this ratio, 0.05, at ${\mathit{R}}_{\mathit{N}}$=11 k\ensuremath{\Omega} is consistent with the picture that fluctuations in the phase of the order parameter dominate the S-I transition in these films.

We present measurements of the temperature dependence of the tunneling density of states near the Fermi energy, G 0 (T) , and resistive transitions, R(T) , of ultrathin PbBi films. Both R(T) and G 0 (T) broaden substantially near the superconductor to insulator transition (SIT). The broadening in R(T) is not affected by the proximity of a ground plane suggesting that long range Coulomb interactions are not important to the SIT. The results suggest that the transport properties of films near the SIT are influenced by fluctuations in both the phase and the amplitude of the order parameter. We discuss the data in terms of recent theories of the superconducting transition in low superfluid density systems.

Granular Pb thin films on the insulating side of the two-dimensional superconductor-insulator transition are observed to exhibit a large negative magnetoresistance and electroresistance (change in resistance with electric field) at low temperatures. At high measurement voltages and low temperatures, the film resistances become temperature independent creating a ``metallic'' state. These phenomena are explained as manifestations of transport due to intergranular quasiparticle tunneling. This explanation might also provide insights into the similar behavior observed in other superconductors.

As the normal state sheet resistance, $R_n$, of a thin film superconductor increases, its superconducting properties degrade. For $R_n\simeq h/4e^2$ superconductivity disappears and a transition to a nonsuperconducting state occurs. We present electron tunneling and transport measurements on ultrathin, homogeneously disordered superconducting films in the vicinity of this transition. The data provide strong evidence that fluctuations in the amplitude of the superconducting order parameter dominate the tunneling density of states and the resistive transitions in this regime. We briefly discuss possible sources of these amplitude fluctuation effects. We also describe how the data suggest a novel picture of the superconductor to nonsuperconductor transition in homogeneous 2D systems., 11 pages, 5 figures

We have observed superconducting properties in three dimensional CuxGe100−x samples with 38⩽x⩽67. Transition temperature Tc is about 0.4 K . Upper critical magnetic field Hc2 has been measured in these samples confirming that they are indeed superconductors. Near the zero field Tco, Hc2 depends linearly on temperature. Our results show robust superconducting properties present in CuGe samples with weakly disorder.

We have measured the magnetic-field dependence, 0\ensuremath{\le}H\ensuremath{\le}8 T, of the resistive transitions R(T) of ultrathin granular superconducting Pb films with normal-state sheet resistances, ${\mathit{R}}_{\mathit{Q}}$\ensuremath{\le}${\mathit{R}}_{\mathit{N}}$\ensuremath{\le}100 k\ensuremath{\Omega}, where ${\mathit{R}}_{\mathit{Q}}$=h/4${\mathit{e}}^{2}$\ensuremath{\simeq}6.45 k\ensuremath{\Omega}. The data suggest that the magnetic-field-induced superconductor-to-insulator transition in these films occurs in a field regime where pair-breaking effects have significantly reduced the amplitude of the superconducting order parameter. We compare our results with those obtained on systems with uniform morphologies.

We quantitatively study the interface resistance in Ni/Nb multilayers fabricated by sputtering system. For a fixed Ni layer thickness in Ni/Nb/Ni trilayers, the superconducting temperature Tc decreases with decreasing Nb thickness. By analyzing the data with the proximity effect, the critical thickness below which superconductivity vanished was deduced. From current perpendicular to plane (CPP) measurement interpreted with a one-band series-resistor model, we obtained the CPP resistivities of Nb and Ni and the unit area resistances of 4.2±0.2 and 1.5±0.4 fΩ m2 for superconducting and normal Ni/Nb interfaces. The transparency parameter is directly calculated in terms of interface resistance.

The behaviors of superconducting transition temperature Tc and upper critical field Hc2 as a function of different superconductor thicknesses have been investigated in Cu50Ni50∕Nb trilayers and multilayers. We deduced superconductor critical thickness, below which superconductivity vanishes, by analyzing the data in terms of proximity theory. The temperature dependence of Hc2 measurement reveals the spatial dimensional crossover and the flux pinning mechanism in the superconductor. A strong pair-breaking effect was observed in the weak ferromagnetic Cu50Ni50 layers from both measurements. We attribute our observation to the high interface transparency between Cu50Ni50 and Nb.

In this study, we investigated the electron transport properties of interface between a ferromagnet and a superconductor with flowing current perpendicular to plan (CPP) at 4.2K in Fe∕Nb multilayers. The CPP resistance increased linearly with layer thickness and with bilayer number. We extracted the unit area resistance value of one pair of interface for superconducting and normal Fe∕Nb by using a series resistor model. Hence, we can quantitatively analyze the interface resistance between Fe and Nb in the diffusive regime.

We present eletron transport measurement that demonstrate that Pb films that are on the insulating side of the two dimensional superconductor to insulator transitions can be made superconducting by depositing a normal metal, Ag, on them.