Hybrid heterostructures with superconducting/antiferromagnetic interfaces

We report on structural, DC, X-ray and neutron studies of hybrid superconducting mesa-heterostructures with a cuprate antiferromagnetic interlayer Ca1-xSrxCuO2 (CSCO). The upper electrode was bilayer Nb/Au superconductor and copper oxide superconductor YBa2Cu3O7 (YBCO) was the bottom electrode. It was experimentally shown that during the epitaxial growth of the two films YBCO and CSCO a charge carrier doping takes place in the CSCO interlayer with a depth about 20 nm. The conductivity of the doped part of CSCO layer is close to the metal type, while the reference CSCO film, deposited directly on NdGaO3 substrate, behaves as Mott insulator with the hopping conductivity. The interface Au/CSCO is clearly seen on bright-field image of the cross-section of heterostructure and gives the main contribution to the total resistance of mesa-heterostructure.Comment: 16 pages, 9 figure

Superconducting current in hybrid structures with an antiferromagnetic interlayer

It is shown experimentally that the superconducting current density in Nb/Au/Ca1 - x Sr (x) CuO2/YBa2Cu3O7 - delta hybrid superconducting heterostructures with a Ca1 - x Sr (x) CuO2 anti-ferromagnetic (AF) cuprate interlayer is anomalously high for interlayer thicknesses d (M) = 10-50 nm and the characteristic damping length for superconducting correlations is on the order of 10 nm. The experimental results are explained on the basis of theoretical analysis of a junction of two superconductors (S\u27 and S) connected by a magnetic multilayer with the AF ordering of magnetization in the layers. It is shown that with such a magnetization ordering, anomalous proximity effect determined by the singlet component of the condensate wavefunction may take place. As a result, the critical currents in S\u27/I/AF/S and S\u27/I/N/S structures (I denotes an insulator, and N, the normal metal) may coincide in order of magnitude even when the thickness of the AF interlayer considerably exceeds the decay length of the condensate wavefunction in ferromagnetic layers

Origin of superstructures in (double) perovskite thin films

We have investigated the origin of superstructure peaks as observed by X-ray diffraction of multiferroic Bi(Fe0.5Cr0.5)O3 thin films grown by pulsed laser deposition on single crystal SrTiO3 substrates. The photon energy dependence of the contrast between the atomic scattering factors of Fe and Cr is used to rule out a chemically ordered double perovskite Bi2FeCrO6 (BFCO). Structural calculations suggest that the experimentally observed superstructure occurs due to unequal cation displacements along the pseudo-cubic [111] direction that mimic the unit cell of the chemically ordered compound. This result helps to clarify discrepancies in the correlations of structural and magnetic order reported for Bi2FeCrO6. The observation of a superstructure in itself is not a sufficient proof of chemical order in double perovskites

Suurten tietomassojen analysointi Apache Hadoopilla

We report on measurements of dc electron transport and microwave dynamics of thin film hybrid Josephson junctions with an oxide antiferromagnetic interlayer. The base superconducting electrode YBaCuO and the antiferromagnetic (AF) interlayer CaSrCuO (with thickness d = 20 - 70 nm) were grown by laser ablation on NdGaO3 substrates. I-V curves were well fitted to RSJ model and had no excess current, ICRN products were of order 0.2 mV at T=4.2 K. We did not observe any noticeable reduction of ICRN with increasing d. Such “tunnellike” behaviour also resulted in appearance of singularities on I-V curve when magnetic field was applied. Oscillating with microwave power integer and half-integer Shapiro steps were registered along with sub-harmonic detector response. Moreover, for some of junctions a “devil” staircase structure was observed on I-V curves and giant noise-like signals were measured in 1-2 GHz band at the certain levels of microwave power. Observed features, noise performance and the impact of the second harmonic in current-phase relation on junction dynamics are discussed taking into account data for structures without AF interlayer

Electron transport and microwave dynamics of hybrid Nb/Au/CaSrCuO/YBaCuO planar Josephson junctions

We report on measurements of dc electron transport and microwave dynamics of thin film hybrid Josephson junctions with an oxide antiferromagnetic interlayer. The base superconducting electrode YBaCuO and the antiferromagnetic (AF) interlayer CaSrCuO (with thickness d = 20 – 70 nm) were grown by laser ablation on NdGaO₃ substrates. I-V curves were well fitted to RSJ model and had no excess current, ICRN products were of order 0.2 mV at T=4.2 K. We did not observe any noticeable reduction of ICRN with increasing d. Such "tunnellike" behaviour also resulted in appearance of singularities on I-V curve when magnetic field was applied. Oscillating with microwave power integer and half-integer Shapiro steps were registered along with sub-harmonic detector response. Moreover, for some of junctions a "devil" staircase structure was observed on I-V curves and giant noise-like signals were measured in 1-2 GHz band at the certain levels of microwave power. Observed features, noise performance and the impact of the second harmonic in current-phase relation on junction dynamics are discussed taking into account data for structures without AF interlayer

High-frequency dynamics of hybrid oxide Josephson heterostructures

We summarize our results on Josephson heterostructures Nb/Au/YBa2Cu3Ox that combine conventional �S� and oxide high-Tc superconductors with a dominant d-wave symmetry of the superconducting order parameter �D�. The heterostructures were fabricated on �001� and �1 1 20� YBa2Cu3Ox films grown by pulsed laser deposition. The structural and surface studies of the �1 1 20� YBa2Cu3Ox thin films reveal nanofaceted surface structure with two facet domain orientations, which are attributed as �001� and �110�-oriented surfaces of YBa2Cu3Ox and result in S/D�001� and S/D�110� nanojunctions formed on the facets. Electrophysical properties of the Nb/Au/YBa2Cu3Ox heterostructures are investigated by the electrical and magnetic measurements at low temperatures and analyzed within the faceting scenario. The superconducting current-phase relation �CPR� of the heterostructures with finite first and second harmonics is derived from the Shapiro steps, which appear in the I-V curves of the heterostructures irradiated at frequencies up to 100 GHz. The experimental positions and amplitudes of the Shapiro steps are explained within the modified resistive Josephson junction model, where the second harmonic of the CPR and capacitance of the Josephson junctions are taken into account. We experimentally observe a crossover from a lumped to a distributed Josephson junction limit for the size of the heterostructures smaller than Josephson penetration depth. The effect is attributed to the variations of the harmonics of the superconducting CPR across the heterojunction, which may give rise to splintered vortices of magnetic flux quantum. Our investigations of parameters and phenomena that are specific for superconductors having d-wave symmetry of the superconducting order parameter may be of importance for applications such as high-frequency detectors and novel elements of a possible quantum computer

Interfaces in superconducting hybrid heterostructures with an antiferromagnetic interlayer

The structural, X-ray diffraction, and electrophysical studies of hybrid superconducting hetero-structures with an interlayer of cuprate antiferromagnetic Ca1 - x Sr (x) CuO2 (CSCO) with the upper electrode Nb/Au and the lower electrode Y(B)a(2)Cu(3)O(7 - delta) (YBCO) have been carried out. It has been experimentally shown that the epitaxial growth of two cuprates, YBCO and CSCO, results in the formation of an interface on which the enrichment of the CSCO interlayer with charge carriers proceeds to a depth of about 20 nm. In this case, the conduction of the enriched CSCO region proves to be closer to metallic, whereas the CSCO film deposited onto the NdGaO3 substrate is a Mott insulator with hopping conduction