B. Shinozaki

Superconducting and Normal State Properties of NiBi3.

The electrical resistivity, heat capacity, superconducting upper critical magnetic field and magnetic susceptibility of NiBi 3 have been measured for the polycrystal and needle crystal. The temperature dependence of the resistivity ρ( T ) above the superconducting transition temperature can be explained by the parallel resistor formula. From ρ( T ), using the sum of two Gruneisen-Bloch functions, we have obtained that the lower main value of the Debye temperature is 70 K and the higher one is 300 K. This is compatible with ω E ≡30.6 K and ω D ≡141 K obtained from the heat capacity using the hybrid Einstein-Debye model. We have compared the angular dependence of the critical magnetic field with that of the effective mass model and found an anisotropic mass ratio m ∥ b / m ⊥ b ≈0.17 for the needle (∥ b -axis) crystal. Almost the same value of 0.14 is also obtained from the analysis of ρ( T ).

Superconductivity in transparent zinc-doped In2O3 films having low carrier density

Abstract Thin polycrystalline zinc-doped indium oxide (In2O3–ZnO) films were prepared by post-annealing amorphous films with various weight concentrations x of ZnO in the range 0x 0.06. We have studied the dependences of the resistivity ρ and Hall coefficient on temperature T and magnetic field H in the range 0.5T 300 K, H6 Tfor 350 nm films annealed in air. Films with 0x0.03 show the superconducting resistive transition. The transition temperature Tc is below 3.3 K and the carrier density n is about 1025–1026 m−3. The annealed In2O3–ZnO films were examined by transmission electron microscopy and x-ray diffraction analysis revealing that the crystallinity of the films depends on the annealing time. We studied the upper critical magnetic field Hc2 (T) for the film with x = 0.01. From the slope of dHc2 /dT, we obtain the coherence length ξ (0) ≈ 10 nm at T = 0 K and a coefficient of electronic heat capacity that is small compared with those of other oxide materials.

Transport properties and microstructures of polycrystalline In2O3–ZnO thin films

We prepared polycrystalline In2O3–ZnO films by post annealing the amorphous films (1.0 wt % ZnO) at 200 °C with various annealing times ta 0≤ta≤20 h. We have measured the electric resistivity and Hall mobility and also observed film structures by not only the x-ray diffraction but also scanning transmission electron microscopy (STEM) with electron energy-loss spectroscopy (EELS). We have found the following: (1) Hall mobility takes the maximum with respect to the carrier density and the annealed films clearly show the superconductivity of which transition temperature increases with increase in ta. (2) The data on EELS spectra mapping of indium plasmon indicate that droplets of the pure indium phase exist on grain boundaries and near the interface between the film and the glass substrate. However, it seems that these droplets do not form an electrical conducting path but contribute to the scattering centers for carrier electrons, from the dispersed distribution of these droplets in STEM-EELS spectra mappin...

Electron-phonon scattering in amorphous In2O3–ZnO films

For amorphous transparent conductive oxide In2O3–ZnO films over a wide range of resistivities ρ, the temperature dependences of ρ and Hall coefficient RH have been measured in the temperature range of 2.0–300 K. The low-resistivity films show a metallic characteristic (dρ/dT>0), although high-resistivity films show an insulating behavior (dρ/dT<0). Even in metallic films, however, the resistivity slightly increases with decreasing temperature below 20 K because of the term ρquanta(T) due to quantum effects. Through a careful analysis, we have found that the ρ(T) of metallic films changes in the form of ρ(T)−ρ0−ρquanta∝ρ0T2 at temperatures below ∼100 K. This temperature dependence can be explained by the interference term ρel-imp-ph between the impurity scattering and the electron-phonon scattering. At temperatures of 20–300 K, it has been found that ρ(T) agrees well with the sum of the Gruneisen–Bloch term ρel-ph(T)=βel-phF(T,Θd) and the term ρel-imp-ph(T)=Bel-imp-phG(T,Θd). From analyses, with the coeffi...

Nonlinear resistivity in the mixed state of superconducting aluminum films

Abstract In order to study the vortex-glass (VG) transition for conventional type-II superconductors, we have investigated the relation between the current density J and the resistivity ρ in the mixed state of aluminum films with different thickness and dirtiness. The aluminum films have the characteristics of lower Tc and longer coherence length in contrast with high-Tc superconductors. The J–ρ isotherms at various external magnetic fields have been analyzed by Fishers VG theory. The data for the dirty thick film and dirty thin film can be well collapsed onto a single function according to the theories for three dimensional (3D) and two dimensional (2D) systems, respectively, with use of vortex-glass transition temperature, and reasonable values of critical exponent determined from the data analysis. However, for the thick clean film, there are some discrepancies between the experiment and 3D scaling theory; very narrow region of liquid phase and a small value of dynamic critical exponent. The reason for the narrow critical region has been discussed from a different viewpoint.

Thickness-tuned superconductor-insulator transitions in quench-condensed Mo and MoRu films

The results of studies on superconductor–insulator transitions are reported for Mo and MoRu films of varying thickness deposited on SiO underlayers and on bare glass. The film samples were quench-condensed on glass substrates held at liquid He temperatures. MoRu films on SiO, which offer the most homogeneous film morphology, showed a critical sheet resistance of transition, Rc, of ~6.7 kΩ. Both series of Mo films on SiO and MoRu films on bare glass had . These values are larger than those previously reported for MoGe, MoSi, and MoC films. For the above films in the insulating region far from the transition, the exponent of the thermally activated resistance ranged from 0.5 to 1.0.

Electron-Phonon Scattering Effects on the Pair Breaking Parameter in Al, Sn and Pb Superconducting Films

The relation between the pair breaking parameter δ and the inelastic scattering rate 1/τ in has been studied for Al(sheet resistance \(R_{\box}<100 \Omega)\), Sn(<70 Ω) and Pb(<3 Ω) films. The δ III F agrees well with δ M independent of materials and dirtiness: The δ III F is determined by the analysis of the excess conductance with adding the correction term to the Maki-Thompson term and δ M is obtained from the relation \(\delta=\pi\hbar\)/8 k B T τ in , where the τ in is determined by the analysis of the magnetoconductance. The \(R_{\box}\) dependence of δ fluc,e-e M for Al and also Sn films, where the electron-phonon inelastic scattering contribution is subtracted experimentally, is in quantitative agreement with theories independent of materials. This implies that the material dependence of coefficients δ 0 and a in the experimental expression \(\delta=\delta_{0}+aR_{\box}\) is caused by e-p in-elastic scattering depending on materials and dirtiness of films.

Magnetoconductance near Superconducting Transition Temperature of Aluminum Films

In the wide range of the magnetic field, the magnetoconductance in thin Al films agrees well with the theory of Santos and Abrahams and also of Maekawa, extending Larkins theory to higher magnetic fields at temperatures slightly above superconducting transition temperature T c . The inelastic scattering rate 1/τ in obtained from magnetoconductance measurements increases rapidly with decreasing temperature near T c . The pair-breaking parameter δ, which is deduced from the measurements and related to the 1/τ in , implies the temperature dependence shown by Patton and also Keller and Korenman. It is about the half of that estimated from the Maki-Thompson contribution to the excess conductance due to fluctuations at zero magnetic field.

Localization and Interaction Effects in Weakly Localized Region in Aluminum Films

The temperature and magnetic field dependence of the electrical conductance σ in thin granular-aluminum films has been measured in the temperature range 4.2–35 K above the superconducting transition temperature. The temperature dependence of conductance σ in zero magnetic field has been compared with a theory including the higher order contribution of the interaction, by evaluating the localization term from the analyses of the magnetoconductance. The σ in zero field agrees with the theory in a temperature of minimum conductance and in the temperature dependence at high temperatures, with a reasonable value of the average matrix element of the Coulomb interaction.

Upward Curvature of the Temperature Dependence of Upper Critical Magnetic Field Perpendicular to Superconducting Aluminum Films

The temperature dependence of the electrical resistance of thin granular aluminum films shows the maximum far above the superconducting transition temperature due to both effects of thermodynamic fluctuations and electron localization, for the film with large normal-state sheet resistance R N . The temperature dependence of the upper critical field or the film with R N ≃10 3 (\(\varOmega\square\)) shows the upward curvature. The results on the upper critical field are explained by a current theory of dirty superconductors including electron localization and electron-electron interactions.