A.I. Golovashkin

Tunneling and critical-magnetic-field study of superconducting NbC thin films

Abstract Electronic characteristics and superconducting-state parameters of NbC thin films prepared by reactive laser beam deposition were studied by tunneling and critical-magnetic-field measurements. For the first time these investigations were made for NbC samples of practically perfect stoichiometric chemical composition and crystal structure. This compound with low-temperature normal resistivity of 4.6 μω∗cm and critical temperature of 12 K was found to be a clean superconductor ( 1 = 36 nm , ξ 0 ∗ = 23 nm ) characterized by an intermediate type of electron-phonon interaction ( λ = 0.91).

High Tc superconducting films grown by magnetron and laser-beam technique

Abstract Polycrystalline and single-crystal films of MBa 2 Cu 3 O 7-x compounds (M=Y, Ho, Eu Sm, Lu, Gd) were synthesized by high pressure magnetron sputtering and pulsed laser-beam evaporation. Perfect structure, smooth surface, T c over 91K, resistivity 4·10 −5 Ohm·cm 2 at 100K and critical current in excess of 5·10 6 A/cm 2 at 77K were achieved for the both preparation methods.

Anomalous thermal expansion of high-Tc superconducting oxide system

Abstract We present the experimental resalts of Ba1−xKxBiO3 and La2−xSrxCuO4 thermal expansion in the wide temperature and concentration intervals. The nature of observed thermal expansion anomalies in these and other HTSC systems is discussed.

Direct determination of electronic density of states N★(EF) for Nb3Sn from upper critical field HC2 and resistivity ϱ

Abstract The electronic density of states at the Fermi level N★(EF) is extracted from the experimental upper critical field HC2 and resistivity ϱ Nb3Sn in terms of anisotropic GLAG theory. The proposed consideration is not confined by dirty superconductor limit and does not require the electronic specific heat coefficient γ or the plasma frequency ωp data, which were used earlier to estimate the N★(EF) of Nb3Sn from HC2. We show, that the anomaly in the −dHC2/dT dependency on ϱ is connected with the N★(EF) change.

Influence of ion irradiation on superconducting properties of YBa2Cu3O7 films

Superconducting films of YBa2Cu3O7 was irradiated by He2+ions. After fluences F > 2 · 1016 ion · cm−2 Tc < 4.2 K. Tc and Jc of these films more sensitive to irradiation than Nb3Sn films.

Strong influence of magnetic field on the thermal expansion anomaly in La2−xSrxCuO4 and Ba1−xKxBiO3 systems

Abstract The strong magnetic field influence on the anomalous (negative) thermal expansion was observed for La 1.9 Sr 0.1 CuO 4 single crystals and Ba 0.6 K 0.4 BiO 3 polycrystals with cubic lattice symmetry. The observed magnetic field influence was the most prominent in the area of negative thermal expansion α at low temperatures. With magnetic field growing (up to 4T) the temperature interval with negative α was decreasing.

Low temperature measurements of Hc2 in HTSC using megagauss magnetic fields

Abstract Measurements of the upper critical fields in YBCO and BSCCO polycrystalline samples and YBCO epitaxial films were carried out at low temperatures in a pulsed ultrahigh magnetic field obtained in a magnetocumulative generator MC-1. The values of the critical fields at 4.2 K were found to be 168±26 T and 200±25 T for YBCO and BSCCO polycrystalline samples, respectively, and 110±10 T for YBCO films.

Destruction of superconductivity in YBa2Cu3O7−x ceramics by ultrahigh magnetic field

Upper critical fields of high-T/sub c/ superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ ceramics were measured in a pulsed magnetic field H/spl ap/300 T generated by magneto-cumulative plant. The presence of a superconducting phase in the cylindrical sample was detected by the appearance of S-like peculiarities on the dM/dt curve at the moment of short-time slowing of the increasing of applied magnetic field. Upper critical fields H/sub C2/ at T=4.2 and 77 K, defined in such a way, are equal to 180/spl plusmn/36 T and 48/spl plusmn/10 T accordingly.

Microwave nonlinear effects in He-cooled superconducting microstrip resonators

Abstract Nonlinear phenomena in superconducting niobium microstrip-like resonators filled by liquid helium are studied in microwaves. The found nonlinear resonance is explained by thermally induced variations of the helium dielectric permittivity caused by the microwave power losses in superconductor. A number of interesting manifestations of this thermal instability have been observed including the parametric pulse generation of the monochromatic microwave signal, generation of acoustic pulses.

Thermal expansion anomaly of MgB2 at low temperatures and magnetic field influence

Abstract The measurements of thermal expansion α ( T ) of MgB 2 were carried out at low temperatures both in zero magnetic field H and at H =36 kOe. The anomalous (negative) thermal expansion and strong magnetic field influence on the α ( T ) was observed. The results indicate the similarity of the anomalous properties of MgB 2 and oxide high temperature superconducting systems.