Search results for "Condensed Matter::Superconductivity"
showing 10 items of 632 documents
Improvement of the critical current density of spark plasma sintered MgB2by C60addition
2010
We investigated the influence of fullerene (C60) addition on the superconducting parameters of MgB2 bulk samples obtained by spark plasma sintering (SPS). It was found that 1.5?wt% C60 addition leads to the reduction of the critical temperature by a few K, whereas the magnetically determined critical current density increases by approximately one order of magnitude in an applied magnetic field H = 70?kOe at temperature T = 10?K. This indicates substitution of B by C in C60 added MgB2 processed by SPS, contrary to some data reported in the literature obtained using conventional methods. For our relatively large specimens, the occurrence of macroscale flux jumps was observed over a wide (H, T…
Preparation, scaling behavior of activation energy, Hall effect, and flux-flow anisotropy of (Hg0.9Re0.1)Ba2CaCu2O6+δHTS thin films
2004
Abstract We have prepared fully textured (Hg0.9Re0.1)Ba2CaCu2O6+δ (HgRe-1212) thin films by pulsed laser deposition (PLD) and post-annealing. The films exhibit sharp superconducting transitions at Tc=124 K with transition width ΔTc≃2 K. Conditions for reproducible film preparation have been found. The resistive transitions have been investigated in magnetic fields up to 8 T (parallel to the c-axis) and 10 T (perpendicular to the c-axis). We have determined the activation energy of thermally activated flux-motion for both magnetic field orientations. The Hall resistivity (ρxy) of HgRe-1212 superconductor thin films has been measured in the ab-plane at 8 T. In the mixed state a power-law beha…
Investigation of the epitaxy of thin YBa2Cu3O7-delta films
1990
Abstract The degree of epitaxy of thin sputtered and laser ablated films have been investigated by Raman spectroscopy. Using the selection rules for Raman scattering for the different phonons in YBa 2 Cu 3 O 7−δ the superconducting films on SrTiO 3 and MgO are found to be epitaxially grown with the c -axis perpendicular to the substrate. On ZrO 2 the films also grow with their c -axis perpendicular to the substrate, but with randomly oriented a / b -directions in the plane of the film.
Trapping of quasiparticles of a nonequilibrium superconductor
2000
We have performed experiments where hot electrons are extracted from a normal metal into a superconductor through a tunnel junction. We have measured the cooling performance of such NIS junctions, especially in the cases where another normal metal electrode, a quasiparticle trap, is attached to the superconductor at different distances from the junction in direct metal-to-metal contact or through an oxide barrier. The direct contact at a submicron distance allows superior thermalization of the superconductor. We have analyzed theoretically the heat transport in this system. From both experiment and theory, it appears that NIS junctions can be used as refrigerators at low temperatures only w…
Raman scattering studies of ultrathin-layer YBa2Cu3O7/PrBa2Cu3O7 superlattices
1994
We present Raman scattering studies ofc-oriented ultrathin-layer superconducting (YBa2Cu3O7) m /(PrBa2Cu3O7) n superlattices. For the superlattice with (m=2,n=1) sequence, Raman spectra reveal a new line in the spectral region around 320 cm−1. It is interpreted as a mode representing a combination of IR optical phonons of the Y-sublayers with an admixture of aB1g type Raman active vibration in the Pr sublayers. This new line, which is similar to those from the interior of the Brillouin zone of the original lattice, does not exhibit superconductivity-induced self-energy effects, although its counterpart in the pure substance does. No additional line is found in the (m=1,n=2) superlattice in …
Refrigeration of a dielectric membrane by superconductor/insulator/normalmetal/insulator/superconductor tunneling
1997
We have applied tunneling of electrons between a normal metal and a superconductor to refrigerate a thin dielectric membrane attached to the normal electrode of a superconductor/ insulator/normal-metal/insulator/superconductor (SINIS) structure. Starting from T≈200 mK, a decrease in temperature of several mK was observed, measured by a separate thermometer on the membrane. It should be straightforward to improve the refrigerator performance to the level of the recently demonstrated SINIS electron cooling method, such that the drop in the lattice temperature would be more than an order of magnitude larger.
Quantum phase slips in superconducting Nb nanowire networks deposited on self-assembled Si templates
2012
Robust porous silicon substrates were employed for generating interconnected networks of superconducting ultrathin Nb nanowires. Scanning electron microscopy analysis was performed to investigate the morphology of the samples, which constitute of polycrystalline single wires with grain size of about 10 nm. The samples exhibit nonzero resistance over a broad temperature range below the critical temperature, fingerprint of phase slippage processes. The transport data are satisfactory reproduced by models describing both thermal and quantum fluctuations of the superconducting order parameter in thin homogeneous superconducting wires.
Efficient electronic cooling in heavily doped silicon by quasiparticle tunneling
2001
Cooling of electrons in a heavily doped silicon by quasiparticle tunneling using a superconductor–semiconductor–superconductor double-Schottky-junction structure is demonstrated at low temperatures. In this work, we use Al as the superconductor and thin silicon-on-insulator (SOI) film as the semiconductor. The electron–phonon coupling is measured for the SOI film and the low value of the coupling is shown to be the origin of the observed significant cooling effect.
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.
Experimental limits of the observation of thermally activated phase-slip mechanism in superconducting nanowires
2007
The shape of experimentally observed $R(T)$ transition of thin superconducting wires is analyzed. From theoretical point of view, broadening of the transition in quasi-one-dimensional superconducting channels is typically associated with phase-slip mechanism. It is shown that such interpretation can be misleading if to consider geometrical inhomogeneity and finite dimensions of real samples studied in experiments. The analysis is based on experimental fact that for many superconducting materials the critical temperature depends on the characteristic dimension of a sample: film thickness or wire cross section.