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By using a focused-ion-beam (FIB) method with Ga ions, we prepared quasi-one-dimensional (q-1D) In/Mo specimens with widths of ≈ 200 nm and ≈ 500 nm from two dimensional (2D) films deposited on a SiO2/Si substrate. We observed the superconducting transition of q-1D In/Mo, whose transition temperature Tc is higher than T c ≈ 3.6 K of a 2D In/Mo specimen on a glass substrate. For specimens fabricated using the FIB method, the element distributions analyzed by energy dispersive x-ray spectroscopy reveal Ga invasion into the q-1D In/Mo region. The gradually changing resistance of q-1D In/Mo at temperatures below Tc can be well explained by the thermal activation phase-slip model with T c = 5.1 K and coherence length ξ ( 0 ) ≈ 9.5 nm .

We investigated transport properties in superconducting NbN thin films for various values of the normal state sheet conductance σN at temperatures above the superconducting transition temperature Tc. The magnetic field dependence of the magnetoconductance Δσ(T, H) data was primarily analyzed using the theoretical expression given by the sum of three contributions due to the Aslamazov–Larkin ΔσAL(T, H, D) and Maki–Thompson ΔσMT(T, H, D, τin) superconducting fluctuations terms, and the electron localization ΔσL(T, H, Dτin) term, where D is the diffusion constant and τin(T) is the electron inelastic scattering time. It was determined that (1) the Δσ(T, H) data are well explained by the theory for wide temperature and magnetic field ranges, regarding τin(T) and the temperature independent D as fitting parameters, and (2) the rate 1/τin(T) at temperatures near Tc shows anomalous decreases with a V-shape from the values based on the theory. This theory indicates a gradual temperature dependence with a U-shape, given by the sum of three dominant terms 1/τfluc(T), 1 / τ e − e ( T ) and 1 / τ e − ph ( T ) , where these terms correspond to superconducting fluctuation, electron–electron scattering and electron–phonon scattering mechanisms. The discrepancy between experimental data and theory suggests the existence of an additional quantum contribution to the rate 1/τin(T), such as that due to the correction of the density of state.

Transport properties have been investigated for the epitaxial superconducting NbN thin films. We analysed the excess conductance σ' ≡ σ(T) - σN by the sum of the Aslamazov-Larkin (AL) and Maki-Thompson (MT) terms for thermal fluctuations above Tc, where the σN ≡1/RsqN is the normal state sheet conductance. We have found that the theoretical expression σ'theo (T) = σ'AL (T) + σ'MT (T,δ) can be well fitted to σ'exp (T) with use of the suitable value of the pair breaking parameter δ in the MT term relating to the inelastic scattering rate 1/τin(T) as δ = πħ/8kBTτin. The rate 1/τin(T) given by the sum of 1/τfluc(T), 1/τe-e(T) and 1/τe-ph (T) is determined from the analysis of the magneto-conductance Δσ = σ(H) – σ(0) by the sum of AL, MT and the localization terms, where the first, second and third terms correspond to the rate due to the superconducting fluctuation effect, electron-electron and electron-phonon interactions, respectively. The RsqN dependence of δ is expressed by δ = δ0 + αRsqN, where the first term δ0 due to 1/τe-ph (T) and the second term due to the sum of 1/τfluc(T) and 1/τe-e(T). Although we obtained a reasonable value of Debye temperature ΘD ≈630 K from the δ0, the magnitude of the α is about 5 times larger than the theoretical value.

We have investigated the lattice orientation of driven vortex matter in amorphous MoGe films. Mode locking experiments in the flux flow state reveal that in addition to the theoretically predicted lattice orientation parallel to the flow direction also the perpendicular orientation occurs. Mapping out the orientations in a phase diagram, the perpendicular orientation is found to dominate the phase diagram covering a wide field and temperature range. Scanning tunneling microscopy images of the vortex lattice frozen from the flux flow state confirm the switching between parallel and perpendicular orientations in the phase diagram. The effect is possibly caused by the influence of the sample edge.

We have investigated the relation among ρ – T characteristics, superconductivity, annealing conditions and the crystallinity of polycrystalline (In 2 O 3 ) 1− x –(ZnO) x films. We annealed as-grown amorphous films in air by changing annealing temperature and time. It is found that the films annealed at 200 °C or 300 °C for a time over 0.5 h shows the superconductivity. Transition temperature T c and the carrier density n are T c n ≈ 10 25 –10 26 m −3 , respectively. Investigations for films with x = 0.01 annealed at 200 °C have revealed that the T c , n and crystallinity depend systematically on annealing time. Further, we consider that there is a suitable annealing time for sharp resistive transition because the transition width becomes wider with longer annealing times. We studied the upper critical magnetic field H c2 ( T ) for the film with different annealing time. From the slope of dH c2 / dT for all films, we have obtained the resistivity ρ dependence of the coherence length ξ (0) at T = 0 K.

We report on the superconducting characteristics of the Indium thin films on molybdenum under-layer as a function of the In film thickness. Our molybdenum under-layer with thickness of 50 A does not cause the occurrence of superconductivity until 1.5 K and the sheet resistance has logarithmic temperature dependence observed in the present investigation. As thickness of In increased, the oscillation phenomenon of T C was observed at early stage of deposition and the value of T C is higher than the that for bulk of In. Furthermore, it is found that with increase of the In thickness, there are large differences of the strengths of the upper critical magnetic field H C2 ( T ), resistivity and T C between films with thickness below and above 100 A. On the other hand, the T C decreases monotonously as sheet resistance increases, when the T C is plotted against sheet resistance. To clarify the relation of superconducting characteristics and the surface structure of the films with different thickness, we have performed surface observation by atomic force microscope. As a result, we have found that the surface changes from homogeneous structure to inhomogeneous (or percolative) structure, when the thickness of in films pass through about 100 A. Superconductivity of In/Mo films with relatively thick-inhomogeneous films cannot be explained in terms of the simple percolation theory. Therefore, we analysis the experimental data of H C2 ( T ) near T C , using a extended Landau–Ginzburg model. It is found out that our In/Mo films must consider some factors; such as, grain size, the distance of grain space, and the strength of couplings between grains.

We have systematically investigated the temperature dependence of resistivity p and Hall coefficient R H of indium zinc oxide films with thickness d=350 nm in the temperature range 2.0 K to 300 K. Specimen films with p≃3-17 μΩ m (300 K) show metallic characteristics (pαT) at temperatures above 100 K. At low temperatures below 20 K, the resistivity slightly increases with decreasing temperature because of the quantum effects in disordered systems. By eliminating carefully quantum effects p quanta and the residual resistivity po, we have found that the resistivity changes in the form of pα poT 2 at temperatures below ≃100 K. This characteristic indicates the existence of resistivity pel-ph-imp due to the interference effect between the impurity scattering and the electron-phonon scattering. It has been found that the temperature dependence of p(T)for all present films agrees well with the sum of the Bloch-Griineisen term ρ el-Ph =βF(T,ΘD) and the interference term ρ el-ph-imp = B el-Ph-imp G(T,ΘD) in a temperature region 20 K to 300 K. From analyses, regarding the coefficients β, B el-Ph-imp , and the Debye temperature Θ D as fitting parameters, we obtain the Θ D ≃970-1060 K and the longitudinal sound velocity νl ≃ 14,000 m/s under some assumptions.

We have investigated flow properties of a current driven, vortex lattice in amorphous MoGe films by mode locking (ML) experiment. ML is a dynamic resonance between a collective velocity modulation of “lattice mode” and a superimposed ac (rf) current on top of a dc current. Tracing the resonance features against magnetic field, we find two specific orientations of lattice flow with respect to the flow direction in the flux-flow state: one is an orientation characterized by a principal axis of the driven lattice parallel to the flow direction, and the other is another orientation where one of the lattice axes is perpendicular to the flow direction.

We report on thickness-tuned superconductor–insulator transitions in amorphous Bi films quench-condensed onto underlayers of Ge, Sb, and SiO. Bi films on Ge and SiO have almost the same values, ∼ 5.2 k Ω of the critical resistance per square at temperatures down to 0.9 K, whereas those on Sb have a larger value of 7.5 k Ω . On the insulating side, the conductance of Bi films on Sb depends logarithmically on temperature in contrast to the thermally activated form of those on SiO and Ge. The results suggest that the peculiar temperature dependence of the resistance per square of Bi films on Sb is the behavior characteristic of an Sb underlayer which becomes insulating from semimetal by quench-condensation.

Isothermal current–voltage ( J – E ) characteristics have been measured for films of lead (Pb)–indium (In) alloys, Pb 100− x In x ( x =8.23, 4.0 and 2.0 wt.%) in the mixed state. The isothermal log J vs. log E curves similar to those characterizing the vortex glass–vortex liquid (VL) transition in copper oxide superconductors have been observed, though the reversibility of magnetization curve for bulk samples in the mixed state could not be detected within the experimental accuracy in the present study. Using Fisher’s theoretical relations, the transition temperature T g ( H ), the static and dynamical critical exponents are determined. The variation of the exponents with H in low magnetic fields reported in high temperature superconductors was not observed. The upper critical magnetic field H c2 ( T ) determined by resistivity vs. temperature in the mixed state increases with increasing In concentration, but the T g ( H ) is almost independent of the In concentration. A region between H c2 ( T ) and T g ( H ) in a plane of H and T , which may be considered as the VL region, becomes wider with increasing In concentration.

We have measured the perpendicular upper critical magnetic field HC2, the excess conductance σ′ due to superconducting fluctuations and the superconducting transition temperature TC in granular aluminum films in the wide range of the sheet resistance R□, 100 Ω ≦R □ ≦15 k Ω . The temperature dependence of HC2 near TC has been analyzed in the form H C2 =H C2 0 1−T/T C n . For relatively low resistance films, the index n is almost unit. However, n decreases steeply at a characteristic resistance R * ≈1.5 k Ω and approaches 0.7 with increase of R□. This value of n agrees with that predicted from the percolation theory taking account of the fractal nature of clusters. With increasing R□ beyond R*, the value of σ′ decreases drastically as compared with that estimated from the sum of Aslamazov–Larkin and Maki–Thompson terms. The sheet resistance dependence of σ′ can be explained qualitatively by a model based on the scaling law of percolation. The value of TC decreases gradually.

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 ).

We have measured the temperature (T) dependence of the resistance per square R for a series of ultrathin Bi films quench-condensed onto different SiO underlayers ranging in thickness from zero to ∼20A. The R-T characteristics of Bi films on a 4.3A-thick layer of SiO are different from those on the layers thicker than 10A, possibly because of the inhomogeneity in Bi films. The results suggest that insufficient thickness of an underlayer causes a larger value of the critical resistance for the superconductor-insulator transition in quench-condensed Bi films.

We have investigated mode locking resonance of a driven vortex lattice in an amorphous MoGe film by means of rf impedance measurements. This technique allows us to detect directly the lattice motion in response to a rf current superimposed on top of a dc current. At low rf currents the resonance appears as jumps (dips) in real (imaginary) part of rf impedance Z. On increasing rf current, the jump height in the real part of Z at a given resonant condition decreases monotonically, whereas the imaginary part of Z exhibits a transformation from the dip to peak behaviors. Namely, the resonant feature changes from capacitive to inductive responses, on increasing rf current. This behavior implies variations in the phase of rf current relative to that of the lattice velocity modulated by the pinning potential.

We have investigated spatial configurations of vortices in superconducting disks of an amorphous MoGe film. A scanning SQUID microscope allows us to image vortices magnetically in the disks. Results on the disks with 56 μm in diameter demonstrate that quasi-symmetric distributions imposed by the circle geometry appear for vorticity up to five. Meanwhile, for vorticity more than six, vortices form shell structures, in which one vortex (two vortices) is located in the center and the others form a ring around.

The magnetoconductivity (MC) of three-dimensional (3D) aluminum films with various dirtiness has been measured in wide ranges of temperature and magnetic field. (1) Near the superconducting transition temperature T c , the MC takes the minimum at a temperature-independent field H m0 . (2) Above H m0 , MC shows H 1/2 dependence. From the detailed analysis of the H dependence of MC, it has been found that the magnitude of the coefficient of H 1/2 can be explained qualitatively by only the sum of contribution from the weak localization and electron–electron interaction. This experimental result indicates that the superconducting thermal fluctuation effect in the field is almost suppressed by this finite field H m0 , of which values are about two times as large as that of the mean-field upper critical field H c2 (0) as we reported for 2D aluminum films. This circumstance is consistent with the observation of a rapid suppression of the excess conductivity around 2 H c2 (0) for 3D type II superconductors by Lue et al. [J.W. Lue, A.G. Montgomery, R.E. Hake, Phys. Rev. B 11 (1975) 3393].

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 Fisher's 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.

For tin–10 at% copper and tin films in a wide range of normal state sheet resistances, R □N , the electrical resistance R □ ( T ) and the excess conductance σ ′( T , H ) due to superconducting fluctuations have been measured. The data on σ ′( T ,0) near T c have been analyzed by the sum of Aslamazov–Larkin and Maki–Thompson terms. It has been found that there is a large difference of δ (pair breaking parameter in the MT term) between the tin–copper and tin films. The difference of R □N -dependence of δ between the two systems can be explained in terms of the contribution δ e–p = π ℏ /8 k B T τ e–p due to the electron–phonon inelastic scattering, by employing Thouless theory for the rate 1/ τ e–p and also the R □N -dependence of the electrical transport properties for each system. An agreement between the experiment and theory suggests that the rate 1/ τ e–p for disordered thin-films is determined by not only electron mean free path l but also resistivity ratio Γ (= ρ 300 K / ρ 4.2 K ).

Measurements of magnetoconductance (MC) have been made on aluminu films up to large magnetic fields. It has been found that (1) near the transition temperature the MC reaches the minimum at a temperature-independent field H m0 ; (2) for films in a wide range of disorder the values of H m0 are about twice that of the mean-field upper critical field H c2 (0); (3) above H m0 , the MC shows ln H dependence. The magnitudes of the coefficient of ln H have been quantitatively explained by only the sum of contributions from the weak localization and electron-electron interaction (orbital effect). This result suggests that the superconducting fluctuation is limited to the magnetic field region below H ≅ H m0 in the phase diagram in the H - T plane. However, the present theory for MC due to the fluctuation cannot explain such a characteristic field H m0 .

The orientation and deformation of moving vortex lattices in the flux-flow state have been investigated in amorphous superconducting NbGe thin films. Employing a mode-locking technique, we detect how moving lattices deform and their orientation changes as a magnetic field is tilted from normal to the film surface. For high tilt angles the lattice orientation is aligned parallely with the tilt direction. Meanwhile for low tilt angles the lattice orientation depends on the vortex velocity and a velocity-induced reorientation occurs. The characteristic velocity for the reorientation varies remarkably as the moving lattices deform. The observed features are consistent with an extended bond-fluctuation theory, revealing that the anisotropic shaking vortex motion is essential for determining the orientation of moving vortex lattices., Comment: 7 pages, 5 figures, in press

The excess conductance σ′ and the magnetoconductance Δσ in a field H due to superconducting fluctuations have been measured at temperatures near Tc for Al films in the wide range of the sheet resistance R □ , 5.8 Ω/□ ⪅- R □ ⪅- 160 Ω/□ . The contributions due to the Maki-Thompson (MT) correction σ′MT and ΔσMT are well described by the recent Reizer theory, which was obtained from reconsidering the theory of Keller and Korenman. As predicted by the recent theory, the dirtiness dependence of σ′MT and ΔσMT of weak-coupling superconducting films is explained by only R□ without any adjustable parameter. The T dependence of σ′ and the T and H dependence of Δσ for all films are satisfactorily explained by theories including the Aslamazov-Larkin contributions, using R□ as the fitting parameter within a factor of 0.7–1.3 of experimentally determined values.

In order to investigate the pair-breaking mechanism in superconducting films superposed with thin normal metal (Au, Ag, or Cu), the inelastic electron scattering rate 1/τ in and the spin-orbit scattering rate 1/τ so have been studied for aluminum films. The rate 1/τ in has been expressed as a sum of three rates 1/τ fluc (electron-fluctuation), 1/τ e-e (electron-electron) and 1/τ e-ph (electron-phonon). It has been found that 1) the effect of superposition on each rate depends on the superposed metals and on preparation conditions of Al film; 2) the rate 1/τ in determines essentially the pair-breaking parameter δ in the Maki-Thompson term for excess conductance, although 1/τ so increases more strongly with heavier superposed metal; and 3) the increment of δ observed in Al/Au films is caused by the enhancement of 1/τ fluc .

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}

In this study, we investigate the dependence of superconducting transition temperature (Tc) on sheet resistance (Rsq) for two series of NbN films with different homogeneities which were prepared on either MgO substrates (NbN/MgO) or MgO substrate covered with a 1nm thick AlN layer (NbN/AlN/MgO). The Rsq-dependent Tc (Tc(Rsq)) behavior of the homogeneous NbN/MgO films could be explained with Finkel'stein's formula, which is based on localization theory using reasonable fitting parameters. On the other hand, the Tc(Rsq) values of the NbN/AlN/MgO films were larger than that of the NbN/MgO films in the region To understand the origin of this deviation from the theory for homogeneous systems, we assumed that the NbN/AlN/MgO films have the potential to form an inhomogeneous percolation structure. To confirm this assumption, the temperature (T) dependence of the upper critical magnetic field ( near Tc was analyzed using the form which is based on classical percolation theory. From the dependence of Rsq ((Rsq)) of both series, it was found that the (Rsq) of the NbN/AlN/MgO films deviates in the region from in a homogeneous NbN/MgO films. By introducing an effective sheet resistance to account for the inhomogeneous structure of the NbN/AlN/MgO films, we were able to qualitatively explain the differences between the Tc(Rsq) behaviors of the two series.

In order to investigate the crossover from a homogeneous behavior to an inhomogeneous (percolative) one, the temperature $T$ and magnetic field $H$ dependence of the sheet resistance ${R}_{◻}$ have been measured for two-dimensional granular aluminum films. Fitting the theory to data on magnetoconductance near ${T}_{C}$ with use of the diffusion constant $D(T)$ as a fitting parameter, we have obtained the anomalous $T$-dependent diffusion constant $D$. From $D(T)$, the electron diffusion index $\ensuremath{\theta}$, a certain critical exponent in the percolation theory, has been obtained. In the relation ${R}_{◻}\ensuremath{-}\ensuremath{\theta}$, the value of $\ensuremath{\theta}$ varies abruptly near $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{k}\ensuremath{\Omega}$. This behavior suggests the abovementioned crossover is similar to our previous results determined from the $T$ dependence of the upper critical magnetic field. For percolative films at $H=5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, we have found the strong ${R}_{◻}$ dependence of the prefactor ${\ensuremath{\alpha}}_{T}$ in the expression $\ensuremath{\sigma}=[{\ensuremath{\alpha}}_{T}{e}^{2}∕(2{\ensuremath{\pi}}^{2}\ensuremath{\hbar})]\mathrm{ln}\phantom{\rule{0.3em}{0ex}}T+{\ensuremath{\sigma}}_{0}$. The relation ${\ensuremath{\alpha}}_{T}\ensuremath{\propto}1∕{R}_{◻}$ can be explained qualitatively by a model of scaling law for percolation.

We investigated the magnetoconductivity Δσ(H)≡1/ρ(H)−1/ρ(0) in a wide range of magnetic fields for three-dimensional indium oxide films doped with zinc, tin, or gallium in the range of resistivity ρ(300K) between 4.1×10−6 Ωm and 1.7×10−3 Ωm. The weak localization theory was fitted to data for Δσ(H) at various temperatures in the range 2.0 K≤T≤50 K by the use of suitable characteristics Dτin(T) and Dτso, where D, τin, and τso are the electron diffusion constant, inelastic scattering time, and spin-orbit (s-o) scattering time, respectively. It was found that (i) for films with a large value of ρ, the sign of Δσ(H) changes from positive to negative with decreasing temperature as a precursor to an anti-weak localization effect; (ii) the ratio τso/τin decreases from ≈4000 to≈4.0 with increasing ρ; (iii) the strong ρ dependence of Dτso cannot be explained by the model with a constant atomic number Z in a formula τso∝1/Z4 proposed by Abrikozov and Gorkov Zh. Eksp. Teor. Fiz. 42, 1088 (1962); [Sov. Phys. JETP 15,...

We have measured the magnetoconductance (MC) defined by Δ σ = σ ( H )− σ (0) of two-dimensional Bi films subjected to a periodic magnetic field H , which is produced by a superconducting intermediate state of thick Pb film placed in the immediate vicinity of metal films. Non-linear H dependence of MC has been observed at low magnetic fields. This is not expected from a simple magnetic distribution of normal (H=H c ) and superconducting ( H =0) domain structure in the intermediate state. For specimen of which Pb film has sharp edges, MC shows the step-like structure. This indicates the strong surface flux pinning effect. On the other hand, in the case of broad edge of Pb film, MC shows the oscillation behavior.

In order to investigate the crossover from the homogeneous behavior to percolative one for two-dimensional system, the temperature T and magnetic field H dependence of the sheet resistance Rsq have been measured for thin granular aluminum films. In a magnetic field of 5 T , the conductance σ decreases with decreasing T as σ=α T e 2 /(2π 2 ℏ) ln T+σ 0 due to weak localization effect. The value of αT decreases when Rsq increases beyond 6∼8 kΩ . In the network which does not contain loops smaller than the phase relaxation length, weak localization effect is considered to be suppressed. We have obtained the anomalous T-dependent diffusion constant D from the analysis of the magnetoconductance above TC with use of the fitting parameter D(T). These behaviors can be explained qualitatively by a model of scaling law for percolation.

The orientation of a vortex lattice in the flux-flow state of an amorphous Mo1−xGex superconducting film is studied by mode-lock experiments. The formation of a hexagonal moving lattice is observed for a wide range of vortex velocity up to ~20 m/s, which is about 1/10 of the critical velocity (~ 200 m/s) at which the flux-flow instability occurs. The orientation of the hexagonal lattice is observed to be either parallel or perpendicular to the flow direction and a reorientation occurs at a characteristic velocity (~ 1 m/s), separating the perpendicular orientation for low velocity from the parallel orientation for high velocity.

We report that temperature dependence of Hall mobility of the strongly disordered films In2O3-ZnO. We made targets by mixing ZnO into In2O3 at the ratio 0.5 ~ 2 wt%. Sputtering those targets on glass substrate by DC magnetron method, amorphous films with 25 nm thickness were obtained. By annealing at T = 150 ~ 350 OC in the air, oxygen defect decreased and the conductance decreased. We obtained films with conductivity 0.2mS/m ~ 300S/m. In the temperature range T = 90~300K, we measured the Hall effect of these films. The density of electron was 4 × 1018 ~ 1.2 × 1022 m−3 at the room temperature. The Hall mobility μH shows the thermal-activation-like temperature dependence μH = AT−1/2 exp(EB/kBT), where EB is activation energy. By fitting, we obtained EB = 60 ~ 86 meV.

We investigated the magneto-conductivity Δ in three dimensional indium zinc oxide films with different resistivity ρ prepared by postannealing in air. The weak localization theory was fitted to data of Δ H) at temperatures below 50K by the use of suitable inelastic scattering time τi(T) and spin-orbit(S-O) scattering time τi. We found the ρ dependences of both times τ and τi in a range 1.5 × 10−3Ω < ρ 300K)

For the polycrystalline (In2O3)-(ZnO) prepared by annealing in air, we investigated the relation among superconductivity, ρ(T) characteristics and preparation conditions. To clarify the distribution of elements, we studied the microstructure by scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). It was found that 1) The films annealed at restricted regions of annealing temperature Ta and time ta show the superconductivity. Transition temperature TC and carrier density n are Tc

We study the effect of annealing in high vacuum on the transport properties for In2O3-ZnO films. We prepared indium zinc oxide films by the DC-magnetron sputtering method using an In2O3-ZnO target (89.3 wt % In2O3 and 10.7 wt % ZnO). The annealing temperature is from 373 to 773K. From the XRD analysis, we find that all as deposited films are amorphous. In addition we find that amorphous films are crystallized by annealing at a temperature above 773 K over 2 hours. The temperature dependence of resistivity ρ of all amorphous films shows metallic behaviour. On the other hand, ρ(T) of poly In2O3-ZnO films shows semi-conducting behaviour. We carry out a detailed analysis of the temperature dependence of Hall mobility. The activation energy Ed has been obtained from the slope of the carrier concentration Ne vs. the inverse temperature plot at high temperatures. We found that the Ed takes values between 0.43 and 0.19 meV. Meanwhile, temperature dependence of Ne for poly-In2O3-ZnO films did not show activation-like behaviour. This behaviour is thought to be causally related to impurity conduction band.

We have investigated the temperature T and magnetic field H dependences of the sheet resistance R□ of thin (In2O3)0.975-(ZnO)0.025 films with different resistivities and carrier densities prepared by postannealing in air at various annealing temperatures Ta. Regarding the magnetoconductance Δσ(H) ≡ 1/R□(H) − 1/R□(0) of films with large values of sheet resistance R□, agreement between weak localization theory and the data cannot be obtained for any value of the localization length L in (T)=Dτ in (T), where D and τin are the diffusion constant and inelastic scattering time, respectively. Taking account of the inhomogeneous morphology confirmed by Scanning Electron Microscopy (SEM) observation, we introduced the effective sheet resistance R□eff given by R□eff = α × R□meas., where the strength of reduction factor α is less than unit, α ⩽ 1. Using a suitable value of α(Ta), we successfully fitted the theory to data for Δσeff(H, T), regarding Lin2(T) as a fitting parameter in the region 2.0 K⩽T ⩽ 50 K. It was confirmed that the rate 1/τin(T) is given by the sum of the electron-electron and electron-phonon inelastic scattering rates.

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...

We have carried out experiments of the thickness-tuned Superconductor-insulator (S-I) transition for amorphous ultra-thin films of various materials. The S-I transition in two-dimensional homogeneous systems has been studied using a wide variety of amorphous films, such as films quench-condensed onto cryogenic substrates and composite material films. The values of critical sheet resistance Rc obtained by many groups for homogeneous films of various materials do not indicate a universal value. Our results indicate that the Rc of Bi, MoRu and AuGe on SiO underlayers have approximately 5.2, 6.7 and 4.9 k Ω respectively. The difference among the values of Rc of the present three films is small in comparison with previous reports of other groups. The decrease in superconducting transition temperature of Bi, MoRu and AuGe films showed similar dependence of normal state sheet resistance below 2kΩ. This behavior can be theoretically explained by the electron-electron effect due to the enhanced Coulomb interactions in a disordered superconductor. On the insulating side, the conductance of the films exhibits temperature dependence as R = Ro exp[(T0/T)x]. The factor x of Bi films have ~ 1 and that of MoRu and AuGe films are ~ 0.5 near the S-I transition. This results may reflect the difference of films structure.

Thin In2O3-ZnO (IZO) films were prepared by DC-magnetron sputtering with changing the weight concentration x of ZnO, 0 ? x ? 0.07. As-grown amorphous IZO films show the metallic characteristic but do not show superconductivity. We have investigated the T and H dependence of the resistivity ? and Hall coefficient for annealed films with thickness d = 350 nm in air. It is found that the films with 0 ? x ? 0.03 show superconductivity. Transition temperature Tc and the carrier density n of these films are ? 2.0 K and 1025 -1026 m-3, respectively. The annealed In2O3-ZnO films were examined by a high resolution transparent electron microscopy. This investigation reveals that films annealed at 300 ?C are sufficient crystalline. There is a difference of crystal structures between the superconducting film and normal film. We studied the upper critical magnetic field HC2 (T) for the film with x = 0.005. From the slope of dHc2/dT, we obtain the coherent length ?(0) ? 100 A at T = 0 K and the coefficient of the electronic heat capacity ? ? 3.2 (J/m3K2) which is small compared with that of other oxide materials.

This work shows the experimental results of the superconductor-insulator (S-I) transition for ultra-thin Bi films in magnetic fields. The quench-condensed (q-c) Bi film onto insulating underlayers have been interpreted to be homogeneous. In contrast, the Bi film without underlayers has been regarded as a granular film. The electrical transport properties of ultra-thin metal films near the S-I transition depend on the structure of the film. In order to confirm the effect of the underlayer to the homogeneity of the superconducting films, we investigate the characteristics of S-I transitions of q-c nominally homogeneous Bi films on underlayers of two insulating materials, SiO, and Sb. Under almost the same deposition condition except for the material of underlayer, we prepared the Bi films by repeating the additional deposition and performed in-situ electrical measurement. It is found that the transport properties near the S-I transitions show the remarkable difference between two films on different underlayers. As for Bi films on SiO, it turned out that the temperature dependence of resistance per square Rsq(T) of the field-tuned transition and the thickness-tuned transition shows similar behavior; it was a thermally activated form. On the other hand, the Rsq(T) of Bi films on Sb for thickness-tuned S-I transition showed logarithmic temperature dependence, but that for field-tuned S-I transition showed a thermally activated form.

We have systematically investigated the temperature dependence of resistivity p and Hall mobility μ of amorphous Zn-doped In2O3 films (350 nm) in the temperature range 2.0 to 300 K. We prepared film specimens with carrier density n ≈ (2 x 1017 − 6 x 1020/cm3) and p ≈ (3 − 4000)μΩcm (300 K) by changing the gas pressure of oxygen during DC-magnetron sputtering. The μ(n) shows the convex characteristic with a broad peak near n ≈ 3 x 1020cm3, taking the value μ ≊ 50cm2/Vs. In the low n region, it has been found that the μ seems to change as μ n1/3 . For films with n ≥ 5 x 1019/cm3, the p(T) shows the metallic behavior between ≈ 20 K and 300 K. On the other hand, for films with n ≤ 1019/cm3, p(T) essentially shows the insulating behavior at whole temperatures. From the analysis of the p(T) in the expression of p(T) = p0 exp(A/Tn) at low temperatures, we obtained that the data is well explained by n = 1/2 for dirty films. The estimated electron mean free path l(4 K) deviates from the linear dependence of l n to decease abruptly near l ≈ 0.2 − 0.4 nm corresponding to the average distance between In and In (or oxygen).

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.

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.

Temperature and magnetic field dependence of the conductance due to superconducting fluctuations has been measured for aluminum films in the wide range of the sheet resistance. With increasingH, the magnetoconductance Δσ takes the minimum atH=Hm0 independent of temperature nearTc,T≳2Tc. AboveHm0, Δσ shows the lnH dependence. Because the coefficient of lnH is well explained by the sum of the localization and the electron-electron interaction (orbital effect, cooper channel), it seems thatHm0 relates to a characteristic magnetic field, above which the fluctuation effect is almost suppressed. It has been shown that the values ofHm0 are about twice as much as the mean-field upper critical fieldsHc2(0) estimated fromHc2(T) nearTc with the dirty-limit model.

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.

By shadow electron microscopy, the critical current density J p has been measured in lead foils with a periodic one-dimensional thickness modulation. The superconducting and normal laminae in the intermediate state are produced to be parallel to the grooves on the specimen surface. The J p in the modulated-surface specimen is larger than that in the flat-surface specimen. The enhancement of J p as a function of temperature shows anomalies at some temperatures where abrupt changes of the laminar structure are observed. These anomalies are attributed to the discontinuous changes of the period of the laminar structure due to redistributions, but not to the increment of the number of the effective pinning centers due to the matching effect.

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 Larkin's 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.

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.

The critical current density of lead foils carrying a transport current parallel to the layers in laminar structure has been measured by observation of flux domain motion. The pinning force density F p is estimated by using the critical state model. The F p obeys the scaling law; F p = H 2 c ( T ) h (1- h ) 2 ( S p / d + B p ), where H c ( T ), h and d are the critical magnetic field, the reduced magnetic field and the specimen thickness, respectively; S p , B p are material constants. The temperature and reduced magnetic field dependences of F p are discussed in comparison with a model in which the interaction between dislocation lines and superconducting-normal domain walls is assumed.