Search results for "current"
showing 10 items of 2224 documents
Measurement and dephasing of a flux qubit due to heat currents
2013
We study a flux qubit, made of a superconducting loop interrupted by three Josephson junctions, which is subject to a temperature gradient. We show that the heat current induced by the temperature gradient, being sensitive to the superconducting phase differences at the junctions, depends significantly on the state of the qubit. We furthermore investigate the impact of the heat current on the coherence properties of the qubit state. We have found that even small temperature gradients can lead to dephasing times of the order of microseconds for the Delft-qubit design.
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…
Macroscopic persistent currents in laser deposited YBa2Cu3O7 films
1989
We have investigated persistent currents in a superconducting YBa2Cu3O7 ring of about 1 cm diameter, which was deposited as c-axis textured film on a SrTiO3 substrate by laser ablation. The currents were registered, via their magnetic field distribution, with a small vibrating pick-up coil. At 77 K persistent currents with negligible decay over 103 s have been observed below a critical current density jc=0.9×105 A/cm2, both for a field-cooled and a zero-field-cooled sample. This demonstrates that it is possible to fabricate dissipationless devices of such films on a relatively large scale.
Superconducting properties of polycrystalline YBCO prepared by a pyrolytic process
1994
Polycrystalline YBCO was prepared by a pyrolytic process starting from citrate and tartrate precursors. The effect of the precursor on the superconducting properties was investigated by means of magnetic measurements using a SQUID magnetometer, a Vibrating-Sample Magnetometer and an a.c. susceptometer. The critical temperature is not affected by the type of precursor (Tc=85 K for both). On the other hand, the precursor plays an important role on the critical current density, which is found to be an order of magnitude higher in the sample obtained from citrates (Jc(77K, H=0)=2.3·104 A/cm2 and 103 A/cm2 for the from-citrate and from-tartrate sample, respectively).
Fabrication of Quasi-One-Dimensional Superconducting Micro- and Nanostructures
2007
Wires capable of conducting electric current are basic blocks of all electronic applications. Of particular interest for nanoelectronics are superconducting elements taking advantage of the superconductor's macroscopic quantum coherence and zero resistance. Recently there appeared indications that due to quantum fluctuations the dissipationless electric current (supercurrent) can be suppressed in ultra-narrow superconducting channels with the effective diameter below approximately 10 nm. In this Review we will describe methods of fabrication of quasi-one-dimensional superconducting micro- and nanowires suitable for electric transport measurements at cryogenic temperatures. In the first sect…
Relation between microstructure and transport properties of epitaxial YBa2Cu3O7-d thin films.
1997
Abstract In order to understand the origin of the high critical current densities observed in thin superconducting films compared to single crystals we measured in several epitaxial YBa 2 Cu 3 O 7−δ thin films the magnetic field and temperature dependence of the superconducting current density j s and the dynamical relaxation rate Q ≡ d ln j s / d ln( d B/ dt ). For all samples we found that (i) the superconducting current density j s is independent of magnetic field up to a certain field B Φ . The value of this field, which is sample dependent, decreases with increasing temperature; (ii) for fields B>B Φ , the superconducting current density falls off as B −1/2 over several decades; (iii) …
Macroscopic persistent currents in laser ablated YBa2Cu3O7-x films
2011
AbstractThin films of YBa2Cu3O7-x have been produced in situ by laser ablation. As the condensation of the superconducting film is done onto hot substrates (600 - 780°C) at high oxygen pressures (~ 1 mbar), this techniques does not require any special postannealing step. Thus the total process time amounts to less than 10 min. Films were found to be polycrystalline with the c-axis preferentially oriented normal to the substrate plane on single crystalline (001) SrTiO3 and (random) ZrO2, as measured by ion channeling (Xmin = 5.5 % on SrTiO3), x-ray scattering and TEM. Complete superconducting transitions above 90 K with transition widths of about 1 K have been observed even on YSZ substrates…
On the determination of vortex creep parameters in superconductors using standard magnetization relaxation data
2011
The relaxation of the irreversible magnetic moment m(t) in YBa2Cu3O7 (YBCO) films was investigated as a function of temperature T and the external magnetic field H along the c axis applied in zero-field cooling conditions, for the determination of vortex creep parameters. The data analysis was performed using the T and current density dependence of the normalized vortex creep activation energy, or by the fit of the m(t) data with the well known interpolation formula in the framework of the general vortex creep equation. It was found that (i) even for specimens with strong static pinning the characteristic pinning energy remains small in the low-T range, where the vortex creep appearing in s…
Preparation and properties of Tl2Ba2CaCu2O8 thin films
1994
Anex situ process has been developed to produce thin superconducting Tl2Ba2CaCu2O8 films. The properties of films grown on different substrates using different annealing regimes were studied. Critical temperatures of 103–107 K were measured on films prepared in a broad range of annealing temperatures on SrTiO3, LaAlO3, and Y-ZrO2 substrates. A critical current density,Jc, of 2×106 A/cm2 at 77 K was measured on LaAlO3. Film morphology was studied by SEM, AFM, and STM.
Transport anisotropy and of thin films
2005
Abstract The resistivity R ( T ) of superconducting UNi 2 Al 3 thin films shows a pronounced dependence on the current direction. Specifically, the superconducting transition temperature T c is directional dependent as well as the influence of the magnetic ordering on the transport properties. Also the upper critical field B c 2 ( Θ , T ) is moderately influenced by the probe current direction. These anisotropies are discussed in the framework of multiband superconductivity. The initial slope of the upper critical field B c 2 ′ ( T ) provides evidence for a spin singlet state.