Search results for "Optical"
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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.
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 …
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.
A penetration depth study on the non-centrosymmetric superconductors Li2(Pd1−xPtx)3B
2008
Abstract We study the superconducting order parameter in the non-centrosymmetric compounds Li 2 (Pd 1− x Pt x ) 3 B ( x =0, 0.3, 0.7 and 1) by measuring magnetic penetration depth λ ( T ). The low temperature λ ( T ) shows a linear temperature dependence for x ⩾0.3, but follows exponential-like behavior for lower Pt contents. These findings suggest that a spin-triplet state might gradually develop with increasing x due to the broken inversion symmetry.
Microwave Properties of Nb/PdNi/Nb Trilayers
2012
We combine wideband (1-20 GHz) Corbino disk and dielectric resonator (8.2 GHz) techniques to study the microwave properties in Nb/PdNi/Nb trilayers, grown by UHV dc magnetron sputtering, composed by Nb layers of nominal thickness $d_S$=15 nm, and a ferromagnetic PdNi layer of thickness $d_F$= 1, 2, 8 and 9 nm. We focus on the vortex state. Magnetic fields up to $H_{c2}$ were applied. The microwave resistivity at fixed $H/H_{c2}$ increases with $d_F$, eventually exceeding the Bardeen Stephen flux flow value.
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.
Microwave Surface Resistance and Upper-Critical-Field Anisotropy of MgB2 Superconductor
2002
The field-induced variations of the microwave surface resistance are investigated in two different samples of powdered MgB2. The experimental results can be justified in the framework of the Coffey and Clem model with fluxons moving in the flux-flow regime, provided that the anisotropy of the upper critical field is taken into due account. Assuming the angular dependence of the upper critical field expected from the anisotropic Ginzburg-Landau theory, we determine the anisotropy factor by fitting the experimental data of the field dependence of the microwave surface resistance. We show that the anisotropy factor is constant in a range of temperatures of about 3 K below Tc and it takes on di…
Time evolution of the microwave second-order response of YBaCuO powder
2003
Transient effects in the microwave second-order response of YBaCuO powder are investigated. The time evolution of the second harmonic signal has been measured for about 300 s after the sample had been exposed to variations of the DC magnetic field. We show that in different time scales the transient response has different origin. In the time scale of milliseconds the transient response of samples in the critical state is ascribable to processes of flux redistribution induced by the switching on/off of the microwave field. At longer times, the time evolution of the second harmonic signal can be ascribed to motion of fluxons induced by the variation of the DC magnetic field. In particular, di…
Superconductivity in the Heusler Family of Intermetallics
2012
Several physical properties of the superconducting Heusler compounds, focusing on two systems (Y, Lu, Sc)Pd2Sn and APd2M, where A=Hf, Zr and M=Al, In, are summarized and compared. The analysis of the data shows the importance of the electron-phonon coupling for superconductivity in this family. We report the superconducting parameters of YPd2Sn, which has the highest Tc among all known Heusler superconductors.
Interference of nonequilibrium quasiparticles in a superconductor
2003
Abstract We have observed an interference of nonequilibrium quasiparticles, injected from a copper electrode into an aluminium loop through a tunnel barrier. At temperatures below 1K the tunnel current at fixed voltage bias is periodically modulated by external magnetic field. The amplitude of the modulation reaches maximum at a bias slightly below the gap energy, and decreases with the further increase of the bias voltage. For a given voltage bias the amplitude of the current oscillations decreases with increase of the temperature and the loop circumference.