Yulii Kislinskii

Electron Transport in Hybrid Superconductor Heterostructures with Manganite Interlayers

Hybrid herostructures comprising an YBa2Cu3Ox (YBCO) high-temperature superconductor (HTS) layer and Nb/Au low-temperature superconductor (LTS) bilayer (with critical HTS and LTS temperatures Tc and T′c, respectively), separated by a thin (dM = 5–20 nm) interlayer of LaMnO3, La0.7Ca0.3MnO3, or La0.7Sr0.3MnO3 manganite have been studied. The electric resistance and magnetic properties of individual (evaporated directly onto the substrate) manganite films and related hybrid herostructures have been measured. Based on quasi-classical equations, analytical expressions for the conductivity of herostructures at T ≤ T′c are obtained in the case of a low-transparency superconductor/manganite interface. It is established that the conductivity of heterostructures is determined by the proximity effect (related to the penetration of a condensate wavefunction from the Nb/Au bilayer to manganite) and depends strongly on interface transparency. At low temperatures (T ≪ Tc′), the conductivity peaks are found at voltages determined by the exchange field of the manganite interlayer. At Tc′ < T < Tc, conductivity features at nearly zero bias voltages are observed, which are related to the superconductivity of the YBCO electrode.

Dynamics of underdamped Josephson junctions with nonsinusoidal current-phase relation

Results on analytical and computational investigations of high frequency dynamics of Josephson junctions, characterized by nonzero capacitance and the second harmonic in the current-phase relation are presented. These attributes each influence on behaviour of integer Shapiro steps and lead to formation of non-integer Shapiro steps. Analytic theory of the integer and non-integer Shapiro steps has been developed for so-called high frequency limit. The analytical and numerical results are compared with experimental data for hybrid heterostructures YBCO/Au/Nb. Detector response for the case of high fluctuation level has been considered as well.

Magnetically dependent superconducting transport in oxide heterostructures with an antiferromagnetic layer

The superconducting current in hybrid superconducting structures Nb/Au/Ca1−xSrxCuO2/YBa2Cu3O7−δ with an antiferromagnetic layer is experimentally shown to have a Josephson nature, and the deviation from the sinusoidal dependence of the superconducting current on the phase difference between superconducting electrodes is about 20% of the second harmonic. These heterostructures are found to have sensitivity to an applied magnetic field that is much higher than that of conventional Josephson junctions. The experimental shape of the magnetic-field dependence of the critical current in the heterostructures differs from the usual Fraunhofer shape by oscillation with a significantly smaller period along a magnetic field.

Current-Phase Relation of Superconductor-Ferromagnet-Superconductor Junctions with a Composite Interlayer

We report on microwave measurements of hybrid superconductor-ferromagnet-superconductor (SFF’S’) junctions with a composite oxide ferromagnetic bilayer with non-collinear magnetizations. Current-phase relation (CPR) of the junction superconducting current has been evaluated as a function of magnetic field. A significant part of the 2nd harmonic in CPR, about 50%, was measured.

Copper Oxide Superconducting/Antiferromagnetic Interface

Superconducting Nb/Au/Ca1-xSrxCuO2/YBa2Cu3O7 mesa-heterostructures were investigated. Dependencies of electrical parameters versus inverse capacitance were measured. A band diagram which takes into account an accumulation of holes in Ca1-xSrxCuO2 interlayer and band bending due to difference of work functions was proposed. The dependencies of electrical parameters were analyzed by examining the quasipartical and superconducting currents.

Hybrid superconducting mesa-heterostructure with manganite-ruthenate interlayer

We present experimental data on Josephson effect in hybrid superconducting mesa-heterostructures (HSMH) with composite manganite-ruthenate interlayer. The HSMH base electrode consisted of the cuprate superconductor YBa 2Cu3O7 grown epitaxially on a NdGaO substrate using laser ablation. The interlayer was composed from in-situ deposited SrRuO3 (F1) and La0.7Sr0.3MnO3 (F2) thin films, each characterized by different directions of magnetization. The top electrode was Nb/Au thin film. A superconducting current was observed when the interlayer thickness was well above the correlation length, determined by the exchange field in F1 and F2. Obtained IC (H) dependences and non-sinusoidal current-phase relation evaluated from microwave measurements are discussed in terms of generation of long-range spin triplet superconducting current component in heterostructures with interfaces of singlet superconductors and bilayer ferromagnetic materials with different spatial directions of magnetization.