Anomalous Proximity Effect Research Articles

Anomalous proximity effect in superconducting oxide structures with an antiferromagnetic layer

The electrophysical parameters of superconductor/antiferromagnetic insulator structures based on the Nb/Au/Ca1−x Sr x CuO2/YBa2Cu3O7−δ hybrid heterostructure have been examined. YBa2Cu3O7−δ and Ca1−x Sr x SuO2 epitaxial films are grown by the laser ablation method on NdGaO3 single crystal substrates, the thickness of the Ca1−x Sr x CuO2 layer varies from 20 to 50 nm, and x = 0.15 and 0.5. The superconducting pair potential in the interface between the YBa2Cu3O7−δ superconductor and Ca1−x Sr x CuO2 antiferromagnet is found to penetrate into the antiferromagnet at distances much larger than the coherence length calculated for the ferromagnetic layer. The critical current of the superconducting transition manufactured at such an interface is highly sensitive to the magnetic field.

Proximity effect in dirty normal metals attachedto p and d wave superconductors

Abstract The conductance in dirty normal metal/superconductor junctions is numerically studied using the recursive Green function method. The proximity effect in dirty normal metals attached to superconductors depends strongly on the pairing symmetries in superconductors because of a zero-energy state forming at junction interfaces. We show the anomalous proximity effect in a p x wave junctions.

Theory of anomalous charge transport and proximity effect in diffusive normal metal/triplet superconductor junctions

Charge transport and proximity effect of a diffusive normal metal/triplet superconductor (DN/TS) junction are studied based on the Keldysh-Nambu quasiclassical Green's function formalism. In triplet superconductor junctions, mid gap Andreev resonant state (MARS) and proximity effect can coexist each other. The local density of states of quasiparticles in DN region has a zero energy peak contrary to the case of singlet unconventional superconductor junctions. This property becomes a novel method to identify the triplet symmetry of unconventional superconductivity.

Anomalous Proximity Effect in an Inhomogeneous Disordered Superconductor

By combining very low temperature scanning tunneling microscopy and spectroscopy on a TiN film we have observed a nonuniform state comprising of superconducting (S) and normal (N) areas. The local density of states displays a spatial dependence between S and N different from the usual proximity effect. We conclude that mesoscopic fluctuations might play a major role in accordance with recent theories describing superconductor-normal-metal quantum transition.

Anomalous Proximity Effect in Gold Coated (110)YBa2Cu3O7−δFilms: Penetration of the Andreev Bound States

Scanning tunneling spectroscopy of (110)YBa(2)Cu(3)O(7-delta)/Au bilayers reveal a proximity effect markedly different from the conventional one. While proximity-induced mini-gaps rarely appear in the Au layer, the Andreev bound states clearly penetrate into the metal. Zero bias conductance peaks are measured on Au layers thinner than 7 nm with a magnitude similar to those detected on the bare superconductor films. The peaks then decay abruptly with Au thickness and disappear above 10 nm. This length is shorter than the normal coherence length and corresponds to the (ballistic) mean free path.

Quasiclassical theory of spontaneous currents at surfaces and interfaces of d-wave superconductors

We investigate the properties of spontaneous currents generated at surfaces and interfaces of d-wave superconductors using the self-consistent quasiclassical Eilenberger equations. The influence of the roughness and reflectivity of the boundaries on the spontaneous current are studied. We show that these have very different effects at the surfaces compared to the interfaces, which reflects the different nature of the time reversal symmetry breaking states in these two systems. We find a signature of the “anomalous proximity effect” at rough d-wave interfaces. We also show that the existence of a subdominant order parameter, which is necessary for time reversal symmetry breaking at the surface, suppresses the spontaneous current generation due to proximity effect at the interface between two superconductors. We associate orbital moments to the spontaneous currents to explain the “superscreening” effect, which seems to be present at all ideal d-wave surfaces and interfaces, where d xy is the favorite subdominant symmetry.

Coherent Electron Transport in Superconducting-Normal Metallic Films

We study the transport properties of a quasi-two-dimensional diffusive normal metal film attached to a superconductor. We demonstrate that the properties of such films can essentially differ from those of quasi-one-dimensional systems: In the presence of the proximity-induced superconductivity in a sufficiently wide film, its conductance may not only increase but also decrease with temperature. We develop a quantitative theory and discuss the physical nature of this effect. Our theory provides a natural explanation for recent experimental findings referred to as the ``anomalous proximity effect.''

Anomalous proximity effect in d-wave superconductors

The anomalous proximity effect between a d-wave superconductor and a surface layer with small electronic mean free path is studied theoretically in the framework of the Eilenberger equations. The angular and spatial structure of the pair potential and the quasiclassical propagators in the interface region is calculated selfconsistently. The variation of the spatially-resolved quasiparticle density of states from the bulk to the surface is studied. It is shown that the isotropic gapless superconducting state is induced in the disordered layer.

Anomalous magnetic properties and proximity effect coupling in VAMAS strands

Anomalously low levels of proximity effect (PE) coupling, as well as an anomalously high paramagnetic tilt, have been found in some of the superconducting multifilamentary strands produced for the Versailles Project on Advanced Materials and Standards (VAMAS). We report on two types of strands that were measured for the 2nd VAMAS intercomparison program on low-frequency (hysteretic) AC loss: (i) a Cu matrix (H-) series with filament diameters ( d f ) ranging from 0.5 μm to 12 μm and (ii) a nominal Cu-10 wt% Ni (l-) series with d f ranging from 0.4 μm to 1 μm. The l-series strands combine anomalously low levels of PE coupling with a strong paramagnetic tilt. Microprobe analysis of the matrix alloy revealed a composition of 10.3 wt% Ni plus 0.78 wt% Mn, which is in agreement with the manufacturer's specification sheets. The paramagnetic tilt can be shown to be due almost entirely to the presence of the Mn which also plays a dominant role in the anomalous PE suppression. The presence of Mn in this nominally Cu-Ni matrix resolves the ‘anomalously’ low coupling and magnetic properties of the l-series strands in a straightforward way. On the other hand, manufacturer's specifications and microprobe analysis showed that the matrix for the H-series strands was pure Cu. These strands also exhibited an anomalously low level of PE coupling but for different reasons, to be discussed. The PE coupling of these strands is compared to those with a variety of other matrices, while attempting to correct for non-matrix-material factors.

Anomalous Proximity Effect in the Nb-BiSb-Nb Junctions

An anomalous proximity effect was observed in coplanar Nb-BiSb-Nb junctions. The effect consists of a considerable increase of the critical current with an increase in the distance between the superconducting electrodes. The effect is explained by the quantum character of Cooper pair transport through the normal region. Some advantages of the application of such junctions are discussed.

Phase coherent transport in hybrid metallic normal/superconducting mesoscopic structures

A review is given of experiments on disordered normal metal mesoscopic structures containing superconducting (S) islands and/or boundaries. The conductance of the structures may either significantly increase ordecrease at the onset of superconductivity (anomalous proximity effect, APE). The Aharonov-Bohm effect is enhanced by several orders of magnitude in normal rings withS-islands (“giant” AB effect). The conductance of a structure, to which anS-wire is attached at two points, oscillates when the phase difference is varied between the latter. The amplitude of the oscillations exceeds the value ofe 2/h by several orders of magnitude. While the oscillations may be attributed to Andreev reflections of quasiparticles, a standard theory does not offer an explanation of APE coexisting with “giant” AB effect.

A percolation model for copper-oxide superconductor-normal-superconductor junctions

A percolation model is proposed to explain the anomalous proximity effect observed in oxide superconductor-normal-superconductor junctions. Randomly distributed Cooper pair regions are assumed in the two-dimensional normal-conducting copper oxide. Supercurrent without phase fluctuation is investigated. Our calculation suggests that the decay length is more than about 10 nm and is independent of temperature, which is consistent with experimental results. The normal state which has experimentally observed localized conduction characteristics can be explained by this model. Therefore, the random distribution of Cooper pair regions seems to explain the transport properties of the normal-conducting copper oxide.