Search results for "Conductor"
showing 10 items of 1270 documents
θ0 thermal Josephson junction
2017
We predict the thermal counterpart of the anomalous Josephson effect in superconductor/ferromagnet/superconductor junctions with non-coplanar magnetic texture. The heat current through the junction is shown to have the phase-sensitive interference component proportional to $\cos(\theta - \theta_0)$, where $\theta$ is the Josephson phase difference and $\theta_0$ is the texture-dependent phase shift. In the generic tri-layer magnetic structure with the spin-filtering tunnel barrier $\theta_0$ is determined by the spin chirality of magnetic configuration and can be considered as the direct manifestation of the energy transport with participation of spin-triplet Cooper pairs. In case of the id…
Electromagnetic behaviour of superconductive amorphous metals
2005
The penetration depth of the magnetic field into an amorphous superconductor is calculated. The ratio of the London penetration depth δL to the electron free path le under zero temperature is above unity for almost all amorphous metals. That is why pure metals, in a superconducting state, change from type I superconductors to type II superconductors during the crystalline–amorphous transition.
Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride
2014
We report on the microwave (mw) properties of coaxial cavities built by using bulk MgB2 superconductor prepared by reactive liquid Mg infiltration technology. We have assembled a homogeneous cavity, by using an outer MgB2 cylinder and an inner MgB2 rod, and a hybrid cavity by using an outer copper cylinder and the same MgB2 rod as inner conductor. By the analysis of the resonance curves, in the different resonant modes, we have determined the microwave surface resistance, Rs, of the MgB2 materials as a function of the temperature and the frequency, in the absence of DC magnetic fields. At T = 4.2 K and f = 2.5 GHz, by a mw pulsed technique, we have determined the quality factor of the homog…
Microwave surface resistance of pristine and neutron-irradiated MgB2 samples in magnetic field
2008
We report on the microwave surface resistance of two polycrystalline Mg11B2 samples; one consists of pristine material, the other has been irradiated at very high neutron fluence. It has already been reported that in the strongly irradiated sample the two gaps merge into a single value. The mw surface resistance has been measured in the linear regime as a function of the temperature and the DC magnetic field, at increasing and decreasing fields. The results obtained in the strongly irradiated sample are quite well justified in the framework of a generalized Coffey and Clem model, in which we take into account the field distribution inside the sample due to the critical state. The results ob…
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…
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.
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…