Search results for "conductivity"
showing 10 items of 1988 documents
Interface transparency and proximity effect in Nb/Cu triple layers realized by sputtering and molecular beam epitaxy
2004
We have investigated, in the framework of the proximity effect theory, the interface transparency T between Nb and Cu in the case of high quality Nb/Cu trilayers fabricated by molecular beam epitaxy (MBE) and sputtering deposition techniques. The obtained T values do not seem to be strongly influenced by the fabrication methods but more by the intrinsic properties of the two metals; a slightly higher value for T has even been deduced for the MBE prepared samples. The proximity effect in these samples has also been studied in the presence of an external magnetic field. In the parallel configuration a significant shift towards lower values of the 2D–3D crossover temperature has been observed …
Influence of micro-structure in the low temperature critical currents of YBa2Cu3O7?? thin films
1996
Epitaxial YBa2Cu3O7−δ films nucleate in c-axis oriented single-crystalline islands. The surface of the single-crystalline SrTiO3 substrates exhibit steps of one third of the YBa2Cu3O7−δ c-axis. These steps generate a mismatch in the island boundaries between the CuO2 superconducting blocks. We show that these defect regions are strong candidates for being the pinning centers responsible for the large critical currents observed in Laser Ablated and Sputtered thin films.
Probing the superconducting state of UPd2Al3 thin films by tunneling spectroscopy
1997
Abstract Giaever-type planar cross junctions of thin films of the heavy fermion superconductor UPd2Al3 and counter-electrodes of Au, Ag and Al were prepared. Tunneling barriers consisting of the native oxide layer of UPd2Al3 and artificial barriers of AlOx and UOx were investigated. The junctions without artificial barrier show a lack of reproducebility. On some junctions a BCS-like tunneling conductivity with a ratio of 2Δ 0 /k B T c ⋍ 3.8 was observed. Using oxidized Al deposited at room temperature as a barrier no substantial increase of the junction resistance occured. With Uraniumoxide a much higher resistance was obtained, but an association of the bias dependent junction conductivity…
Microrefrigeration by quasiparticle tunnelling in NIS and SIS junctions
2000
Abstract A solid-state refrigeration method at sub-kelvin temperatures has been developed. It is based on quasiparticle tunnelling between a superconductor and a normal metal, or, between two dissimilar superconducting metals. The refrigerator is fabricated by combining nanolithography and micromachining methods. This technique has been demonstrated in both electron cooling from 0.3 to 0.1 K and in refrigeration of a dielectric platform. We describe a new fabrication method of tunnel junctions in a shadow evaporation configuration using a mechanical mask of silicon nitride.
Vortex-system ordering during magnetisation measurements in YBa2Cu3O7−δ films at low temperatures
2007
Abstract Zero-field-cooling dc magnetisation relaxation measurements performed on optimally doped epitaxial YBa 2 Cu 3 O 7− δ films with the external magnetic field H oriented parallel to the c -axis reveal the ordering of the creeping vortex-system in the low temperature T domain, due to the macroscopic currents induced in the sample. This dynamic ordering manifests itself through the appearance of a maximum in the T variation of the normalised vortex-creep activation energy. The location of this maximum in the H – T plane describes a well-defined current induced order–disorder line. Our results suggest the absence of a static elastic vortex glass in disordered high-temperature superconduc…
Response time of a thermometer based on normal metal–insulator–superconductor (NIS) tunnel junctions
2003
Abstract We have measured the thermal response of a superconductor–normal metal–superconductor (SINIS) tunnel junction structure at substrate temperature ∼60 mK by directly heating the electron system in the normal metal island. In our structure, we find the response time is determined by the electron–phonon coupling in the electron temperature range 300– 600 mK . By using AC heating, the cut-off frequency caused by this response time has been measured, showing that SINIS structures operate as a thermometer up to a few MHz in this temperature range.
Heat capacity of small superconducting disks
2000
Abstract The superconducting state of small samples in a magnetic field is strongly dependent on the sample dimensions and geometry. We have initiated measurements of heat capacity of small superconducting disks. Our method, extensively used in many of our related experiments, is to measure the thermal time constant as a function of temperature of disks on a thin silicon nitride membrane. Theoretical results on heat capacity of the disks based on the Ginzburg–Landau theory will be presented.
Crystal Structure of Heusler Compounds
2013
Heusler compounds are promising materials in many fields of contemporary research. The spectrum of their possible applications ranges from magnetic and magneto-mechanical materials over semiconductors and thermoelectrics to superconductors. An important feature of the Heusler compounds is the possibility of controlling the valence electron concentration by partial substitution of elements. On the other hand, the properties also depend on the degree of ordering of the crystal structure. In general, Heusler compounds crystallize in the Cu2MnAl-type structure but in many cases certain types of disorder are observed. In this chapter, a detailed description of the crystal structure as well as di…
Preparation of thin films of the heavy fermion superconductor UNi2Al3
2004
Abstract Thin films of the heavy fermion superconductor UNi 2 Al 3 were prepared by coevaporation of the elementary components in an MBE-system. We obtained textured (1 0 0)-oriented films of this hexagonal compound depositing on Al 2 O 3 substrates. Epitaxial growth was observed on (1 1 2)-oriented orthorhombical YAlO 3 substrates. However, due to pronounced strain the UNi 2 Al 3 (1 0 0)-axis is shortened by ≈2%. No superconductivity of the films was observed which can be associated with the high impurity concentration deduced from R ( T ) and XRD investigations.
Vortex creep crossover in YBCO/PrBCO superlattices during standard magnetization relaxation measurements
2011
We investigated the relaxation of the irreversible magnetization in a series of 200?nm thick YBa2Cu3O7/PrBa2Cu3O7 [(YBCO)n/(PrBCO)m] superlattices, where the thickness m of the nonsuperconducting PrBCO layer (measured in unit cells) was kept to m = 4 (sufficient to decouple the superconducting YBCO layers), whereas the thickness n of the YBCO layer was varied between 2 and 20 unit cells. The analysis of standard zero-field-cooling dc magnetization relaxation data obtained in the low temperature T region with the applied magnetic field H oriented along the c axis reveals the occurrence of a crossover elastic (collective) vortex creep at low T?plastic vortex creep at high T, generated by the …