Search results for "Transition temperature"
showing 10 items of 137 documents
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.
Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system.
2015
A superconductor is a material that can conduct electricity without resistance below a superconducting transition temperature, Tc. The highest Tc that has been achieved to date is in the copper oxide system: 133 kelvin at ambient pressure and 164 kelvin at high pressures. As the nature of superconductivity in these materials is still not fully understood (they are not conventional superconductors), the prospects for achieving still higher transition temperatures by this route are not clear. In contrast, the Bardeen-Cooper-Schrieffer theory of conventional superconductivity gives a guide for achieving high Tc with no theoretical upper bound--all that is needed is a favourable combination of …
Anisotropic transport properties ofUNi2Al3thin films
2007
Experimental results on the transport anisotropy in thin films of the heavy fermion superconductor $\mathrm{U}{\mathrm{Ni}}_{2}{\mathrm{Al}}_{3}$ are presented. They show that the eletronic transport in $\mathrm{U}{\mathrm{Ni}}_{2}{\mathrm{Al}}_{3}$ for different directions is strongly dominated by different sheets of the Fermi surface, and that the magnetic moments must be assigned to a cylindrical part around the $c$ axis. Founded on the findings about the Fermi surface, the dependence of the resistive superconducting transition temperature ${T}_{c}$ on the current direction in $\mathrm{U}{\mathrm{Ni}}_{2}{\mathrm{Al}}_{3}$ can be explained as the result of weakly coupled superconducting …
Location of the mean-field critical temperature of underdopedYBa2Cu3Oyfilms
2007
We determined the Berezinskii-Kosterlitz-Thouless transition temperature ${T}_{\mathit{KT}}$ at the superconducting layer level and the mean-field critical temperature ${T}_{c0}$ in oxygen-deficient $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ films ($y\ensuremath{\sim}6.5$, 6.55, and 6.65). We used the $T$ dependence of the quasi-two-dimensional $I\text{\ensuremath{-}}V$ exponent for $T\ensuremath{\leqslant}{T}_{\mathit{KT}}$, and the analysis of the resistive transition in the framework of the Ginzburg-Landau two-dimensional Coulomb gas model for $Tg{T}_{\mathit{KT}}$. Both procedures give essentially the same results, with ${T}_{c0}$ remaining in the domain of the elect…
Confined and extended optical phonons in an ultrathin-layerYBa2Cu3O7/PrBa2Cu3O7superlattice
1995
Raman-scattering studies of a high-quality ultrathin-layer (${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$${)}_{4}$/(${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$${)}_{1}$ superconducting superlattice resolve, in addition to the combined ${\mathit{B}}_{1\mathit{u}}$ mode at 310 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ previously reported for a 2:1 sample, a peak at 350 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at low temperature. This peak and also others have been interpreted by a lattice-dynamical calculation for the superlattice. The results are compared with confined or extended phonon pictures. The superlattice mode is not renormalized below the superconducti…
Superconductivity in palladium-based Heusler compounds
2009
This work reports on four more Heusler superconductors: ${\text{Pd}}_{2}\text{ZrAl}$, ${\text{Pd}}_{2}\text{HfAl}$, ${\text{Pd}}_{2}\text{ZrIn}$, and ${\text{Pd}}_{2}\text{HfIn}$. These compounds exhibit superconducting transition temperatures ranging from 2.4--3.8 K as determined by resistivity measurements. According to their behavior in an external magnetic field, all compounds are type II bulk superconductors. The occurrence of superconductivity was predicted for these compounds using electronic structure calculations. The electronic structures exhibit van Hove singularities (saddle points) at the $L$ point. These lead to a maximum in the corresponding density of states and superconduct…
Vortex–antivortex unbinding in oxygen-deficient YBa2Cu3O7− films
2007
Abstract In-plane zero-magnetic-field current–voltage ( I – V ) characteristics of oxygen-deficient YBa 2 Cu 3 O 7− δ films (7 − δ ∼6.5, 6.55, and 6.65) were thoroughly investigated. A good agreement with the quasi two-dimensional (2D) vortex–antivortex unbinding scenario was observed, similar to the behaviour of highly anisotropic Bi 2 Sr 2 CaCu 2 O 8+ δ films. The temperature variation of the I – V exponent allows the determination of the Berezinskii–Kosterlitz–Thouless transition temperature T KT at the superconducting Cu–O layer level, and the mean-field critical temperature T c0 . We found that both T KT and T c0 increase with increasing doping, and T c0 remains in the region of the …
Effect of zero-point motion on the superconducting transition temperature of PdH(D)
1984
Using self-consistent density functional formalism we show that the electronic structure of PdH(D) is influenced by the zero-point vibration of hydrogen and deuterium. This quantum effect makes a small but significant contribution to the superconducting transition temperature ${T}_{c}$ of PdH(D). The reverse isotope effect on ${T}_{c}$ is found to be dominated by the changes in the force constants between PdH and PdD.
Josephson junctions and superconducting field effect transistors based on epitaxial Bi2Sr2Can-1CunO2(n+2) thin films
1998
Abstract Josephson junctions based on thin films of the Bi2Sr2Ca2Cu3O10+δ compound show IcRn products compatible with YBa2Cu3O7−δ samples. Using quasiparticle tunneling experiments we found evidence for a superconductor–insulator–superconductor tunneling process via localized states in the barrier. The Bi2Sr2CaCu2O8+δ compound is investigated regarding possible applications in superconducting field effect devices. We present thin films of four unit cells thickness that are superconducting at 58 K. An inverted metal–insulator–superconductor structure was prepared. From the modulation of the normal state resistance we estimate a carrier density of 7×1019 cm−3 for a superconducting sample. The…
Continuous Phase Transitions at Surfaces of CuAu Alloy Models — A Monte Carlo Study of Surface Induced Order and Disorder
1996
The influence of surface on phase transitions has found significant attention in recent years, and a number of excellent reviews exists. [1, 2, 3] A variety of complex phenomena occur which are also related to the physics of adsorption and wetting. The scenario of wetting requires three distinct phases, for instance the vacuum, the bulk phase and a third phase intervening in between at equilibrium. In case of surface induced disorder (SID, a film of disordered layers at the surface “wets” the bulk phase as the temperature approaches the bulk transition temperature T c,b. The transition at the surface may be continuous (standard critical wetting phenomena), and, as theoretically investigated…