Critical current in a system of two superconductors connected by a short small-diameter normal metal bridge

It is shown that states with phase increments δ?>π can form in superconductor-narrowing (normal metal)-superconductor systems. If the conditions a?l?ξ(0), where a is the cross-sectional size of the narrowing, l is the length of narrowing, and ξ(0) is the correlation radius at zero temperature, are satisfied, there is a region of parameters (a, l, ξ(0), T) in which the critical current is attained in solutions with a phase difference δ?>π.     

Theoretical study of photoinduced superconductors in a two band model

A study of photoinduced high-T_c superconductivity is presented by canonical two-band BCS model containing Fermi surfaces of p and d holes. We have obtained two superconducting gaps from this model. Studies of chemical potential and hole concentration dependences on critical temperature (T_c) are made. The enhancement of T_c is found due to doping.The study of specific heat and density of states based on this model is also presented. The dependence T_c(n_h) for the system YBa₂Cu₃O_7?x (1 2 3) obtained theoretically agrees with the available experimental data.     

Gravitational force between two electrons in superconductors

The attractive gravitational force between two electrons in superconductors is deduced from the Eddington–Dirac large number relation, together with Beck and Mackey electromagnetic model of vacuum energy in superconductors. This force is estimated to be weaker than the gravitational attraction between two electrons in the vacuum.     

Coupling of two superconductors through a ferromagnet: evidence for a pi junction

We report measurements of the temperature dependence of the critical current, I(c), in Josephson junctions consisting of conventional superconducting banks of Nb and a weakly ferromagnetic interlayer of a CuxNi1-x alloy, with x around 0.5. With decreasing temperature I(c) generally increases, but for specific thicknesses of the ferromagnetic interlayer, a maximum is found followed by a strong decrease down to zero, after which I(c) rises again. Such a sharp cusp can be explained only by assuming that the junction changes from a 0-phase state at high temperatures to a pi phase state at low temperatures.     

On the relation between two models for superconductors with a structural distortion

Two three-dimensional models exhibiting coexistence of superconductivity and lattice distortion are discussed. One of the models, studied in detail by Rusinov, Do Chan Kat and Kopayev, takes into account the superconductivity inter- and intra-band pairing phenomenologically. The other has been derived by Mattis and Langer from a Fröhlich-type hamiltonian by eliminating the linear electron-phonon coupling in the presence of a “condensing” phonon mode. Both approaches are shown to agree in the limit ω_D å μ, where ω_D is the cut-off energy and ω is the deviation of the chemical potential from the band centre.     

Phenomenological description of the two energy scales in underdoped cuprate superconductors

Raman and angle-resolved photoemission spectroscopy experiments have demonstrated that in superconducting underdoped cuprates nodal and antinodal regions are characterized by two energy scales instead of the one expected in BCS theory. The nodal scale decreases with underdoping while the antinodal one increases. Contrary to the behavior expected for an increasing energy scale, the antinodal Raman intensity decreases with decreasing doping. Using the Yang-Rice-Zhang model, we show that these features are a consequence of the nonconventional nature of the superconducting state in which superconductivity and pseudogap correlations are both present and compete for the phase space.     

Local density of states around two nonmagnetic impurities in cuprate superconductors

The local density of states (LDOS) around two nonmagnetic impurities which are located at different sites is studied within the two-dimensional t-J-U model. The order parameters are determined in a self-consistent way with the Gutzwiller projected mean-field approximation and the Bogoliubov-de Gennes theory. When the two impurities are located one or two sites away, we find the superconductivity coherence peaks are more strongly suppressed and the zero-energy peak (ZEP) has split into two peaks. Whereas when the two impurities are located next to each other, the ZEP vanished, and LDOS does not change a lot compared with the case away from the impurities.     

High Tc superconductors based on Y-Ba-Cu-O system

Preliminary studies on the high T superconductivity encountered in the yttrium or^c rare earth-barium-copper-oxygen system are reported. Zero resistance T_c of 95K has been realized.     

Video detection of mm-waves via photon-assisted tunneling between two superconductors

Photon-assisted tunneling between two superconductors has been used for sensitive detection of mm-wave radiation with best current responsivity of about half the quantum limit e/. The best NEP referring to the whole system is some 10^–15 W and about 10^–15 W referring to the junction alone.     

Lattice gas dynamics: application to driven vortices in two dimensional superconductors

A continuous time Monte Carlo lattice gas dynamics is developed to model driven steady states of vortices in two dimensional superconducting networks. Dramatic differences are found when compared to a simpler Metropolis dynamics. Subtle finite size effects are found at low temperature, with a moving smectic that becomes unstable to an anisotropic liquid on sufficiently large length scales.     

Conductance fluctuations in disordered superconductors with broken time-reversal symmetry near two dimensions

We extend the analysis of the conductance fluctuations in disordered metals by Altshuler, Kravtsov, and Lerner (AKL) to disordered superconductors with broken time-reversal symmetry in d=(2+?)$d=(2+\mathrm{?})$ dimensions (symmetry classes C and D of Altland and Zirnbauer). Using a perturbative renormalization group analysis of the corresponding non-linear sigma model (NLσM) we compute the anomalous scaling dimensions of the dominant scalar operators with 2s   gradients to one-loop order. We show that, in analogy with the result of AKL for ordinary, metallic systems (Wigner–Dyson classes), an infinite number of high-gradient operators would become relevant (in the renormalization group sense) near two dimensions if contributions beyond one-loop order are ignored. We explore the possibility to compare, in symmetry class D, the ?=(2−d)$\mathrm{?}=(2-d)$ expansion in d<2$d<2$ with exact results in one dimension. The method we use to perform the one-loop renormalization analysis is valid for general symmetric spaces of Kähler type, and suggests that this is a generic property of the perturbative treatment of NLσMs defined on Riemannian symmetric target spaces.     

Investigation of stimulated dynamics in strongly anisotropic high-temperature superconductors system Bi-Pb-Sr-Ca-Cu-O

It is used the mechanical method of Abrikosov vortex stimulated dynamics investigation in superconductors. With its help it was studied relaxation phenomena in vortex matter of high-temperature superconductors. It established that pulsed magnetic fields change the course of relaxation processes taking place in vortex matter. The study of the influence of magnetic pulses differing by their durations and amplitudes on vortex system of strongly anisotropic high-temperature superconductors system Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O_10−δ showed the presence of threshold phenomena. The small duration pulses do not change the course of relaxation processes taking place in vortex matter. When the duration of pulses exceeds some critical value (threshold), then their influence changes the course of relaxation process which is revealed by stepwise change of relaxing mechanical moment τrel. These investigations showed that the time for formatting of Abrikosov vortex lattice in Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O_10−δ is of the order of 150 μs which on the order of value exceeds the time necessary for formation of a single vortex observed in isotropic high-temperature superconductor HoBa₂Cu₃O_7−δ and on two orders exceeds the creation time of a single vortex observed in classical type II superconductors.     

Supercooling across first-order phase transitions in vortex matter

Hysteresis in cycling through first-order phase transitions in vortex matter, akin to the well-studied phenomenon of supercooling of water, has been discussed in literature. Hysteresis can be seen while varying either temperature T or magnetic field H (and thus the density of vortices). Our recent work on phase transitions with two control variables shows that the observable region of metastability of the supercooled phase would depend on the path followed in H-T space, and will be larger when T is lowered at constant H compared to the case when H is lowered at constant T. We discuss the effect of isothermal field variations on metastable supercooled states produced by field-cooling. This path dependence is not a priori applicable to metastability caused by reduced diffusivity or hindered kinetics.     

Charge imbalance due to thermoelectric effects in superconductors: A two fluid description

Using a generalised two-fluid picture for the charge of a superconductor, the generation of charge imbalance by a temperature gradient under different conditions is studied. The voltage developed by a temperature gradient in the presence of supercurrent is estimated. The results agree with experiment. The results obtained for the generation of charge imbalance in the absence of imposed current agree with those obtained using other techniques.     

Quantum correlations in a system of two two-level atoms

The dynamics of appearance of a steady entangled state in an ensemble of two collectively decaying two-level atoms is studied on the basis of the Peres-Horodecki criterion with regard to the dipole-dipole interaction between the atoms and their frequency detuning. It is ascertained that, in the absence of dipole-dipole interaction, the steady-state entanglement is in many respects due to the coincidence of the frequencies of transitions in the atoms, whereas a difference in the frequencies, related to different positions of the atoms in a crystal or their thermal motion, destroys the steady-state entanglement. Upon a dipole-dipole interaction, a steady-state entanglement also exists and, in this case, depends strongly on the relationship between the magnitude of the dipole-dipole interaction, the constant of coupling with a thermostat, and the phase of the resonance wave; the entanglement appears only when the thermostat coupling constant is dominant.     

Transition radiation in a system of two cascaded gratings

Transition radiation that arises when a charged particle passes through two consecutive plane gratings is considered. The gratings are made up of parallel metal wires. The planes of the gratings are parallel to each other and perpendicular to the direction of motion of the particle. The conductors of one of the gratings are perpendicular to the conductors of the other. It is shown that the generated transition radiation has elliptic polarization; the ellipticity and the sign of rotation depend on the angle of radiation, the distance between the gratings, and the velocity of the charged particle.