Superconductor Sandwich Research Articles

The Investigation of Critical Temperature Tc of Homophase Superconductors Bi1.7Pb0.3Sr2Ca(n– 1)CunOy (n = 3, 4, 5) and Current–Voltage Characteristics of InP Semiconductor–Bi/Pb Superconductor (2223, 2234, 2245) Sandwich Pairs

The electrophysical properties of semiconductor–superconductor sandwich pairs (InP–Bi/Pb 2223, 2234, 2245) are investigated, in which homophase superconductors based on bismuth cuprates with high reproducible critical temperatures of superconducting transition Tc = 107–180 K are used. The advantage of melt solar technology for obtaining superconducting materials is demonstrated. The microstructure and phase composition of strongly anisotropic superconductors with nominal composition Bi1.7Pb0.3Sr2Ca(n– 1)CunOy (n = 3, 4, 5) are researched. A technique of experimental determination of superconducting transition critical temperatures Tc in single-phase and homophase HTSC samples is presented. The current–voltage characteristics of InP–Bi/Pb pairs are investigated. The relationship between the electrical resistance of sandwich pairs and superconductor critical temperature Tc is established.

Исследование критической температуры T-=SUB=-c-=/SUB=- гомофазных сверхпроводников (Bi-=SUB=-1.7-=/SUB=-Pb-=SUB=-0.3-=/SUB=-Sr-=SUB=-2-=/SUB=-Ca-=SUB=-(n-1)-=/SUB=-Cu-=SUB=-n-=/SUB=- O-=SUB=-y-=/SUB=- (n=3, 4, 5) и вольт-амперных характеристик сэндвич-пар полупроводник InP-сверхпроводник Bi/Pb (2223, 2234, 2245)

AbstractThe electrophysical properties of semiconductor–superconductor sandwich pairs (InP–Bi/Pb 2223, 2234, 2245) are investigated, in which homophase superconductors based on bismuth cuprates with high reproducible critical temperatures of superconducting transition T _ c = 107–180 K are used. The advantage of melt solar technology for obtaining superconducting materials is demonstrated. The microstructure and phase composition of strongly anisotropic superconductors with nominal composition Bi_1.7Pb_0.3Sr_2Ca_( n _– 1)Cu_ n O_ y ( n = 3, 4, 5) are researched. A technique of experimental determination of superconducting transition critical temperatures T _ c in single-phase and homophase HTSC samples is presented. The current–voltage characteristics of InP–Bi/Pb pairs are investigated. The relationship between the electrical resistance of sandwich pairs and superconductor critical temperature T _ c is established.

Supercurrent through a polyamidine film

We have investigated the temperature dependence of the conductivity of polyamidine films with different contact area between electrode and polymer surface at low temperatures. At low temperatures we observed a decreasing conductivity as well as a supercurrent flow through the polyamidine film in superconductor–polyamidine–superconductor sandwich structures with film thickness about 1μm.

Nb/Al/AlO x / AlO x / Al/Nb Josephson junctions for programmable voltage standards

We present a study of the microwave characteristics of Josephson junctions based on a superconductor–insulator–normal–insulator–superconductor sandwich, fabricated in Nb/Al/AlOx technology. With the nonhysteretic Shapiro steps and the small parameter spread observed, the junctions are suitable for programmable Josephson voltage standards. Their characteristic voltage Vc≈100 μV enables operation at microwave frequencies up to 100 GHz.

Quantum levels and quasi-local states of SINIS structures

Quantum states of a superconductor–insulator–normal metal–insulator–superconductor sandwich (the SINIS structure) are investigated on the basis of the Bogoliubov–de Gennes equations. The dispersion equation is obtained for the quasiparticle spectrum for energies E<Δ (Δ is the energy gap in the superconductor) taking into account the Andreev scattering as well as conventional electron reflection at the interfaces of the SINIS structure. The spectrum makes it possible to calculate the Josephson current in the system. The transparency coefficient of the system for electrons with a continuous energy spectrum is calculated, and quasi-local states (“resonance levels” of transparency) are determined for the structure under investigation.

Conductive Polymer / Superconductor Sandwich Structures

ABSTRACTMethods for characterizing the interface of conductive polymer/high-Tc superconductor sandwich structures are reported. Electrochemical procedures, such as cyclic voltammetry and chronoamperometry, are utilized to deposit conductive polymers directly onto bulk ceramic and thin film samples of YBa2Cu3O7-δ. Moreover, similar methods are utilized to cycle the polymer structures between their neutral (non-conductive) and oxidized (conductive) forms. Through changes in the polymer doping level, the superconducting properties of the high-Tc component can be modulated in a controllable and reproducible fashion. This paper focuses on an analysis of conductive polymer/superconductor interface phenomena as explored by electrochemical, resistivity vs. temperature and contact resistance measurements.

Critical field of a superconductor—normal-metal—superconductor junction

We have computed the lower critical field H/sub c/1 of a superconductor--normal-metal--superconductor sandwich as a function of normal-metal thickness. The Ginzburg-Landau free-energy functional is minimized by varying the order parameter while computing the magnetic field exactly by numerical means. Good agreement with Pb-Cd sandwiches is found with no adjustable parameters. Comparison is also made with a previous calculation of H/sub c/1 for the large-thickness limit.

Boundary resistance of the superconducting-normal interface

The resistances of superconductor---normal-metal---superconductor sandwiches have been measured in which the mean free path of the superconductor was greater than or comparable with the coherence length. Below about 0.5 ${T}_{c}$, the resistance was nearly independent of temperature and, to within the experimental error, equal to the estimated resistance of the normal layer, indicating that there was relatively little interface contamination. At temperatures above about 0.9 ${T}_{c}$ the resistance rose rapidly as the temperature was increased towards ${T}_{c}$. A theory for this rise, based on the normal metal-insulator-superconductor tunneling theory of Tinkham and Clarke, is used to calculate the quasiparticle charge imbalance, ${Q}^{*}$, injected into the superconductor from the normal layer. The resultant additional boundary voltage per unit current is expressed as a boundary resistance ${R}_{b}=\frac{Z(T){(D{\ensuremath{\tau}}_{{Q}^{*}})}^{\frac{1}{2}}{\ensuremath{\rho}}_{S}}{A}$, where $Z(T)$ is a universal function of temperature, and $D$, ${\ensuremath{\tau}}_{{Q}^{*}}$, ${\ensuremath{\rho}}_{S}$, and $A$ are the electron diffusion coefficient, the charge relaxation time, the normal-state resistivity, and the cross-section area of the superconductor. Above 0.9 ${T}_{c}$, the data are an excellent fit to the theory if one takes ${\ensuremath{\tau}}_{{Q}^{*}}=\frac{4{k}_{B}T{\ensuremath{\tau}}_{E=0}({T}_{c})}{\ensuremath{\pi}{\ensuremath{\Delta}}_{\ensuremath{\infty}}(T)}$, where ${\ensuremath{\tau}}_{E=0}({T}_{c})$ is the inelastic-scattering time at the Fermi surface at ${T}_{c}$, and ${\ensuremath{\Delta}}_{\ensuremath{\infty}}(T)$ is the energy gap far from the interface. The inferred values of ${\ensuremath{\tau}}_{E=0}({T}_{c})$ in ${\mathrm{Pb}}_{0.99}$${\mathrm{Bi}}_{0.01}$, Sn, ${\mathrm{Sn}}_{0.99}$${\mathrm{In}}_{0.01}$, and In, 0.25 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$ s, 2.6 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$ s, 1.1 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$ s, and 1.1 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$ s, respectively, are generally in good agreement with the computed values of Kaplan et al.

Bound States in Normal-Metal—Superconductor Sandwiches: Magnetic Field Dependence and Estimate of Fermi Velocities in Zinc

The pair potential well, produced in a normal metal by proximity with a superconductor, supports bound states which can be observed in a tunneling experiment. Such states have been observed in Pb/Zn-zinc oxide-Pb, and the temperature dependence of the I–V characteristic has been reported. Here these experiments are continued, showing, in particular, the magnetic field dependence of the bound states. The dressed Fermi velocities along the c axis of zinc are estimated to range from 0.4×108 to 1.0×108 cm/sec, but to obtain improved accuracy in this measurement cleaner and thicker Zn films are required.