Single Crystal Superconductor Research Articles

An EXAFS study of SrCaBiCuO superconductor

We have measured the Cu K edge EXAFS of BiCaSrCuO single crystal superconductor and semiconductor, the nearest coordination around Cu of superconductor phase is agreement with the results obtained from single crystal X-ray diffraction by Sunshine et. al. [1]

High field measurements of whole profile of H c and normal resistivity of high-T c single crystal superconductors

The whole profiles of H c2- T and the normal-state resistivity curves of the high- T c single crystal superconductors (RBa 2Cu 3O y, R = Eu, Dy, Ho) are measured under pulsed magnetic fields up to 50 T. The H c2- T curves agree well with the dirty-limit BCS result and the normal-state resistivities show metallic characteristics.

A new configuration of mixed state observed in superconducting single crystal YBa 2Cu 3O 7− x

A kind of new cylindric configuration of mixed state was observed in YBa 2Cu 3O 7− x single crystal superconductors at77K by Bitter decoration method.

Superconducting phases in Bi-Sr-Ca-Cu-O system

The preparation and characterization in structure and chemistry of the superconducting phases in Bi-Sr-Ca-Cu-O system are briefly summarized. The growth of the 85 K single crystal superconductor Bi2Sr2CaCu2Oy is outlined. The measurement of the anisotropic normal-state resistivities of the 85 K superconducting single crystal is presented in detail and the analysis of the incommensurate modulation in this compound is also given.

Pair potential for a weak-coupling, single-crystal superconductor

In the standard treatment of weak-coupling superconductors, the pair potential enters as a nondiagonal but local potential. It is shown that for a pure, weak-coupling, bulk, single-crystal superconductor the quasiparticle wave functions are then Bloch functions and the self-consistent pair potential is periodic in space with the periodicity of the crystal structure. The relation between this periodic character of the pair potential and energy gap structure is discussed, and it is pointed out that energy gap structure of the general character expected appears to have been observed. The validity of a local pair potential is also briefly considered.

Measurements of Ultrasonic Velocities Using a Digital Averaging Technique

A new pulse-echo technique using real-time digital averaging is described for measuring the phase velocity in solids up to 50 MHz. The technique can measure the transit time between any two echoes to an absolute accuracy of 0.1 nsec and measure small changes in transit time to a sensitivity of 20 psec. Experimental examples are given based upon ultrasonic velocity measurements in a single crystal superconductor.

Selection Rules for Tunneling into Single-Crystal Superconductors

The first conclusive evidence for a tunneling selection rule for single-crystal superconductors is presented. Using tunneling data for the (001) plane of gallium obtained in two different laboratories, we show that the zero transverse $k$-vector rule of Dowman, Mac-Vicar, and Waldram is superior to the usual group-velocity rule. The dominant tunnel direction in real space is the normal to the tunnel barrier and does not appear to be affected by barrier orientation or structure.

Effects of energy gap anisotropy in pure superconductors

Various effects of anisotropy of the superconducting energy gap are theoretically considered. In order to estimate the effects of anisotropy upon the thermodynamic properties of pure, single-crystal superconductors, a factorable BCS-like model for the effective electron-electron matrix element V pp′ = (1 + a p ) V(1 + a p′ ) is used. The effects of anisotropy upon the temperature dependence of the gap parameter, the critical field, and the specific heat near the critical temperature are then shown to be small and proportional to the mean-squared anisotropy 〈 a 2〉, which is of the order of 0.02 for typical superconductors. Theoretical expressions which explicitly include the anisotropy of a general gap parameter are given for low-temperature specific heat, nuclear spin-lattice relaxation time, tunneling, surface resistance, and longitudinal ultrasonic attenuation. These processes are seen to be more sensitive to the details of the anisotropy than are the above thermodynamic properties.