Dynamics of the Josephson Multi-Junction Systems with Junctions Characterized by Non-Sinusoidal Current - Phase Relationship

It is shown that the inclusion of junctions characterized by non-sinusoidal current - phase relationship in the systems composed of multiple Josephson junctions - results in the appearance of additional system phase states. Numerical simulations and stability considerations confirm that these phase states can be realized in practice. Moreover, spontaneous formation of the grain boundary junctions in high-T$\text{}_{c}$ superconductors with non-trivial current-phase relations due to the d-wave symmetry of the order parameter is probable. Switching between the phase states of multiple grain boundary junction systems can lead to additional 1/f noise in high-T$\text{}_{c}$ superconductors

Effect of the In-Plane Epitaxial Mismatch between the Substrate and the Film on the Properties of YBa2\text{}_{2}Cu3\text{}_{3}O7−δ\text{}_{7-δ} Films

We study the effect of the in-plane epitaxial mismatch between the substrate and the film on the crystallographic structure and the transport properties of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7-δ}$ superconducting films of thicknesses ranging between 600 and 3000Å. The films are grown by pulsed laser deposition on the new type of single-crystalline substrates prepared by Czochralski method, with the chemical formula (SrAl$\text{}_{0.5}$Ta$\text{}_{0.5}$O$\text{}_{3}$)$\text{}_{0.7}$(CaAl$\text{}_{0.5}$Ta$\text{}_{0.5}$O$\text{}_{3}$)$\text{}_{0 .1}$(LaAlO$\text{}_{3}$)$\text{}_{0.2}$. We find that superconducting properties of the samples are excellent, and generally they improve with increasing of the film thickness as a result of improved structural ordering. We also investigate the influence of the film thickness on the behavior of the critical current densities

Study of excimer laser irradiation effects on properties of crystalline YBaCuO thin films

The influence of UV laser irradiation on the physical properties of epitaxial YBa2CU3O7-delta thin (< 1 mum) films fabricated by laser ablation was studied. The samples were irradiated by pulsed excimer laser beam at different incident energy densities E-ir less than or equal to 130 mJ/cm(2), i.e. 2-3 times below the ablation threshold of YBaCuO. The analysis of the sample cross-section using transmission electron microscope shows that such irradiation forms a disordered layer on the top of the crystalline film. Sample surface amorphization was observed also by atomic force microscope. Due to strong UV irradiation absorption in YBaCuO this surface layer acts like a protective cover for the sample interior. Only a small reduction of superconducting critical temperature T-c was observed. Both transport measurements in normal state and magneto-optical studies in superconducting state indicate that between the disordered layer and the bottom non-modified part of the film there exists a wide transitional region with reduced carrier concentratio

Effect of pulsed UV laser irradiation on the properties of crystalline YBa2Cu3O7− thin films

International audienceThe influence of UV laser irradiation on the physical properties of epitaxial YBa2Cu3O7-δ (YBCO) thin (<1 µm) films fabricated by laser ablation was studied. The samples were irradiated by a pulsed excimer laser beam at different incident energy densities Eir≤160 mJ cm-2, i.e. 2–3 times below the ablation threshold of YBCO. Analysis of the sample cross-section using a transmission electron microscope (TEM) has shown that such irradiation results in a disordered layer on the top of the film. Independent confirmation of the film surface amorphization was also obtained by tunnelling experiments. Strong UV absorption in YBCO prevents further spreading of the amorphous region, which can be considered as a protective layer for the sample interior. Only a small reduction of the superconducting critical temperature Tc was observed in the irradiated samples. The transport measurements in the normal state indicate that at the interface between the disordered layer and the non-modified part of the film there exists a wide transitional region with reduced carrier concentratio

Magnetic Properties of FeSeTe Compound Crystallized from Liquid Phase

We report on measurements of samples with nominal composition $FeSe_{0.5}Te_{0.5}$, crystallized by the Bridgman method. Magnetic and transport properties of the samples were examined. The measurements confirm the coexistence of ferromagnetism and superconductivity below the superconducting transition temperature. The ferromagnetic contribution to magnetization, estimated at 10%, might be caused by the presence of ferrimagnetic $Fe_7Se_8$, which occupies about 10% of sample volume. From the Andreev spectroscopy we found superconducting energy gap Δ = 2.6 meV at T = 4.2 K, and from magnetization measurements the critical temperature $T_c$ = 15.8 K. The critical current density in magnetic field H = 4 kOe, determined from magnetization measurements, is $j_c$ = (1-2) × 1$0^4$ A/$cm^2$ and weakly depends on magnetic field intensity

Magnetic field penetration in MgB2 single crystals: Pinning and Meissner holes

The evolution of flux distribution in MgB2 single crystals during their remagnetization was imaged with magneto-optical technique. Meissner holes, formed as the areas where the annihilation of vortices and antivortices takes place, were found at the boundary between oppositely magnetized parts of the crystal. Gradient of magnetic induction in the vicinity of Meissner holes was found to be enhanced. Finger-like structures of convex shape, formed during the penetration of magnetic flux inside the crystal, were observed and explained as an effect of inhomogeneous pinning and demagnetizing field redistribution in the sample. (C) 2014 AIP Publishing LLC