Quasiparticle Relaxation Rates in a spatially inhomogeneous superconductor

Effective quasi-particle relaxation rates in reduced gap regions of a dirty superconductor (S) at low temperatures are calculated from microscopic theory

Superconductivity and magnetic ordering in the mixed ternary ErxY1−xRh1.1Sn3.6 system

The superconducting transition temperature Tc as well as the magnetic ordering temperature Tm have been determined in the mixed ternary compound ErxY1−xRh1.1Sn3.6 as a function of the Er concentration. Tc decreases from 3.13 K for YRh1.1Sn3.6 to 1.1K for ErRh1.1Sn3.6. Reentrant superconductivity has been found for x > 0.6.\ud \ud The application of the models of Abrikosov and Gorkov, Maekawa and Tachiki, and Roshen and Ruvalds to this system is discussed. Tc as function of the concentration x is best described by the model of Roshen and Ruvalds assuming a ferromagnetic interaction between the spins. The parameter I2N(0), arising from electron spin, is found to be 0.088 K. The ferromagnetic ordering temperature dependence is described by the theory of Oguchi and Ono, using an effective coordination number z = 6 and an exchange constant of J′ = 0.30 K

On the suppression of the sidelobes of the supercurrent in small Josephson tunnel junctions

The critical currents of Nb/Al, Al-oxide, Al/Nb tunnel junctions of various shapes have been measured as a function of the applied magnetic field. For the square junction and for some special shapes like the diamond, ¿1 + cosine¿ and quartic junctions the Ic(B) pattern falls off theoretically as 1/Bn, with n respectively equal to 1, 2, 3 and 4. In general the measurements are in good agreement with the theoretical predictions. For the "1 + cosine" and quartic shapes we found a sidelobe suppression that is even larger than that obtained in theory. For the quartic junction the first sidelobe is only 0.3% of the zero-field current. An Ic(B) modulation with a small, only slowly decreasing amplitude is observed for the diamond, "1 + cosine", and quartic junctions, that can be explained by rounding of the sharp edges of the junction shapes, due to the fabrication process

Conductance studies on different types of Nb/Al, AlOx,(/A1)/Nb Josephson tunnel junctions

The conductance-voltage characteristics of different types of Josephson tunnel junctions have been measured at 4.2 K: symmetric Nb/Al, AlOx/Al/Nb, asymmetric Nb/Al, AlOx/Nb and Nb/Al/AlOx-/AlOx/Nb, containing a double oxidation layer. The symmetric junctions can be described very well by a trapezoidal potential barrier model. The asymmetric junctions show less agreement with theory. In these junctions resistance switching occurs, possibly due to charge trapping. The resistance is lower than in symmetric junctions. The conductance measurements on double oxidation layer junctions show, that this type of junction has an inhomogeneous oxide layer

Josephson junctions and DC SQUIDS based on Nb/Al technology

A process for fabricating high-quality Josephson junctions and DC SQUIDS on basis of Nb/Al technology has been developed. DC magnetron sputtering is used for the deposition of the metal layers and the barrier is formed by thermal oxidation of the Al-layer. The junction area of 5 µm × 5 5 µm is obtained using anodisation. Three types of Josephson tunnel junctions have been prepared: standard Nb/Al, AlOx/Nb, symmetric Nb/Al, AlOx, Al/Nb and Nb/Al, AlOx/AlOx/Nb, the latter having a double oxide layer. We performed current-voltage and conductance-voltage measurements at different temperatures and special attention was paid to the noise behaviour. Gap and sub-gap parameters as well as barrier parameters are presented. Three different DC SQUID configurations were developed on basis of the Nb/Al Josephson junctions. The measured characteristics of the standard Tesche-Clarke DC SQUID, the resistively shunted SQUID and the inductively shunted SQUID are compared with special attention being paid to the noise properties. A 19-channel DC SQUID magnetometer with standard and/or resistively-shunted DC SQUIDs is under construction

X-ray response of tunnel junctions with a trapping layer

The use of trapping layers in superconductive tunnel junctions may drastically improve their functioning as X-ray detectors. Information about these trapping layers can be obtained from I/V-curves and X-ray spectra. The application of a magnetic field causes a substantial reduction of the bandgap in the trapping layer

Enhanced piezoelectric properties of (110)-oriented PbZr1−xTixO3 epitaxial thin films on silicon substrates at shifted morphotropic phase boundary

Piezoelectrical, ferroelectrical, and structural properties of epitaxial pseudocubic (110)pc oriented 500 nm thick PbZr1−xTixO3 thin films, prepared by pulsed laser deposition on (001) silicon substrates, were measured as a function of composition. The dependence of the measurement data on the Ti content is explained by an abrupt transition from the rhombohedral r-phase to the tetragonal (c/a) 45 phase for x  ≈  0.6, indicating a shift of the Morphotropic Phase Boundary to this value, where the effective piezoelectric coefficient e3 1 ,eff and dielectric constant ε33 ,eff reach their maximum values. These findings are of great significance for Si-based piezo-micro electro mechanical systems, in particular energy harvesters. The largest value of the figure-of-merit for such devices was found for x  = 0.6, FOM=24.0 GP