Search results for "superconductor"
showing 10 items of 93 documents
Vortex instability and vortex-glass transition in Bi 2 Sr 2 CaCu 2 O 8 and YBa 2 Cu 3 O 7 thin films
2000
We investigated the current-voltage (I-V) curves of high-T c superconductors at very low and very high dissipation levels. In the limit of low driving currents the barriers for vortex movement become infinite in the vortex-glass state. Using long measurement bridges up to 0.5 m we were able to sample an electric field range from 1 V/m down to 10 -8 V/m in one experimental setup. The resulting I-V curves allowed us to verify an excellent glass scaling of the I-V curves, which revealed an increased dynamical exponent of the glass transition. We also found a considerable dependence of the vortex-glass scaling on the probed electric-field range. At very high dissipation levels the I-V curves of…
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…
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.
Application of superconductor-semiconductor Schottky barrier for electron cooling
2003
Abstract Electronic cooling in superconductor–semiconductor–superconductor structures at sub kelvin temperatures has been demonstrated. Effect of the carrier concentration in the semiconductor on performance of the micro-cooler has been investigated.
Vortex motion in Nb/PdNi/Nb trilayers: new aspects in the flux flow state
2011
We study the dynamics of vortex lines in Supercondutor/Ferromagnet/Superconductor (SFS) heterostructures at microwave frequencies. We have employed swept-frequency, Corbino-disk and resonant, dielectric-resonator techniques to obtain the field and temperature dependence of the vortex-state parameters. We concentrate here on the genuine flux-flow resistivity $\rho_{ff}$, that we access at subcritical currents using a sufficiently high driving frequency. We find that $\rho_{ff}$ does not follow the well-known Bardeen-Stephen model. Instead, it is well described by a full time-dependent Ginzburg-Landau expression at very thin F layer thickness, but changes to a previously unreported field-depe…
Shift of the surface-barrier part of the irreversibility line due to columnar defects in Bi2Sr2CaCu2O8 thin films
2003
We report the results of studying the influence of the uranium-ion irradiation of the Bi_2Sr_2CaCu_2O_8 thin films on the high-temperature part (close to critical temperature) of their irreversibility line. We studied irreversible properties of the films by measuring the hysteresis of nonresonant microwave absorption. The results have revealed the shift of irreversibility line towards low temperatures and magnetic fields. The effect is most significant for the films irradiated with large doses, more than 1T. This fact is in good agreement with the theoretical prediction by Koshelev and Vinokur of suppression of surface barrier by columnar defects.
Cooling of a superconductor by quasiparticle tunneling
1999
We have extended the cryogenic cooling method based on tunneling between a superconductor and another metal to the case when both metals are superconducting but when their energy gaps are different; earlier, this method was applied between a superconductor and a normal metal. The electron system of a titanium strip with the superconducting transition temperature Tc2=0.51 K has been cooled from 1.02Tc2 to below 0.7Tc2 by this method, using aluminum as the other superconductor.
Surface-barrier effects in the microwave second-harmonic response of superconductors in the mixed state
2005
We report on transient effects in the microwave second-harmonic response of different type of superconductors in the mixed state. The samples have contemporarily been exposed to a dc magnetic field, varying with a constant rate of 60 Oe/s, and a pulsed microwave magnetic field. The time evolution of the signal radiated at the second-harmonic frequency of the driving field has been measured for about 500 s from the instant in which the dc-field sweep has been stopped, with sampling time of ∼0.3 s. We show that the second-harmonic signal exhibits two relaxation regimes; an initial exponential decay, which endures roughly 10 s, and a logarithmic decay in the time scale of minutes. Evidence is …
Nonlinear current-voltage characteristics due to quantum tunneling of phase slips in superconducting Nb nanowire networks
2013
We report on the transport properties of an array of N about 30 interconnected Nb nanowires, grown by sputtering on robust porous Si substrates. The analyzed system exhibits a broad resistive transition in zero magnetic field, H, and highly nonlinear V(I) characteristics as a function of H which can be both consistently described by quantum tunneling of phase slips.
Comparison among superconducting models for β″-ET4[(H3O)Fe(C2O4)3]·C6H5Br single crystals by scanning tunnelling spectroscopy
2008
Single crystals of the novel superconductor beta ''-(BEDT-TTF)(4)[(H3O)Fe(C2O4)(3)]center dot C6H5Br charge-transfer salt were studied using a scanning tunnelling microscope. The measured samples have an onset critical temperature of about 4.0 K. Features often reported on similar compounds were observed in the tunnelling spectra at 1.4 K. STS spectra are compared with several models for the superconducting density of states. Our analysis evidences inhomogeneous superconductivity and indicates that the presence of a magnetic layer into the sample plays a role in determining the superconducting spectroscopic features. (C) 2008 Elsevier Masson SAS. All rights reserved.