Search results for "Condensed Matter::Superconductivity"
showing 10 items of 632 documents
Complete stabilization and improvement of the characteristics of tunnel junctions by thermal annealing
2006
We have observed that submicron sized Al--AlO{$_x$}--Al tunnel junctions can be stabilized completely by annealing them in vacuum at temperatures between $350^{\circ}$C and $450^{\circ}$C. In addition, low temperature characterization of the samples after the annealing treatment showed a marked improvement of the tunneling characteristics due to disappearance of unwanted resonances in the current. Charging energy, tunneling resistance, barrier thickness and height all increase after the treatment. The superconducting gap is not affected, but supercurrent is reduced in accordance with the increase of tunneling resistance.
Superconductivity with broken time-reversal symmetry inside a superconducting s-wave state
2018
In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors, in which superconductivity may coexist with magnetism, and only a few examples are known, when superconductivity itself induces spontaneous magnetism. The most known compounds are Sr$_2$RuO$_4$ and some noncentrosymmetric superconductors. Here, we report the finding of a narrow dome of a novel $s+is'$ superconducting (SC) phase with broken time-reversal symmetry (BTRS) inside the broad $s$-wave SC region of the centrosymmetric multiband superconductor Ba$_{\rm 1-x}$K$_{\rm x}$Fe$_2$As$_2$ ($0.7 \lesssim x \lesssim 0.85$). We observe spontaneous magnetic fields …
Proximity-induced Josephson-quasiparticle process in a single-electron transistor
1998
We have performed the first experiments in a superconductor - normal metal - superconductor single electron transistor in which there is an extra superconducting strip partially overlapping the normal metal island in good metal-to-metal contact. Superconducting proximity effect gives rise to current peaks at voltages below the quasiparticle threshold. We interpret these peaks in terms of the Josephson-quasiparticle process and discuss their connection with the proximity induced energy gap in the normal metal island.
Dynamics of a Ferromagnetic Particle Levitated Over a Superconductor
2018
Under conditions where the angular momentum of a ferromagnetic particle is dominated by intrinsic spin, applied torque is predicted to cause gyroscopic precession of the particle. If the particle is sufficiently isolated from the environment, a measurement of spin precession can potentially yield sensitivity to torque beyond the standard quantum limit. Levitation of a micron-scale ferromagnetic particle above a superconductor is a possible method of near frictionless suspension enabling observation of ferromagnetic particle precession and ultrasensitive torque measurements. We experimentally investigate the dynamics of a micron-scale ferromagnetic particle levitated above a superconducting …
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.
Andreev Reflection at Point Contacts with Heavy-FermionUBe13?
2000
We comment on a recent Letter by Waelti et al. (PRL 84, 5616 (2000)) on 'Spectroscopic evidence for unconventional superconductivity in UBe13'. We show - by using the basic Wexler formula - that it is unlikely to observe Andreev reflection at point contacts between UBe13 and a normal metal. The large superconducting anomalies usually found for those contacts are mainly due to the resistive Maxwell resistance vanishing below Tc of UBe13.
Time evolution of the microwave second-harmonic response of MgB2 superconductor
2003
We report on transient effects in the microwave second-order response of two ceramic MgB2 samples. The time evolution of the second-harmonic signal is investigated for about 500 s after the sample has been exposed to a variation of the dc magnetic field. We suggest that during the first seconds the response is determined by diffusive motion of fluxons, while in the time scale of minutes it is ruled by magnetic relaxation over the surface barrier.
Force-free state in a superconducting single crystal and angle-dependent vortex helical instability
2017
Superconducting 2H-NbSe2 single crystals show intrinsic low pinning values. Therefore, they are ideal materials with which to explore fundamental properties of vortices. (V, I) characteristics are the experimental data we have used to investigate the dissipation mechanisms in a rectangular shape 2H-NbSe2 single crystal. Particularly, we have studied dissipation behavior with magnetic fields applied in the plane of the crystal and parallel to the injected currents, i.e. in the force-free state where the vortex helical instability governs the vortex dynamics. In this regime, the data follow the elliptic critical state model and the voltage dissipation shows an exponential dependence.Moreover,…
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…