Iu. M. Dmitrenko

Commensurability effect and lock-in transition in Mo/Si superconducting superlattices

We report the first observation of the lock-in transition in artificial superconducting superlattices, which takes place in tilted magnetic fields. The measurements were carried out on the Mo/Si layered system. The temperature dependence of the critical angle for the trapping of the vortices in the orientation parallel to the layer planes is determined by the previously known resistive method and by a new method based on the effect of commensurability between the intervortex distance and the superlattice wavelength. The temperature dependences of the critical angle obtained by the two methods practically coincide. The experimental results are consistent with the theoretical predictions of Feinberg and Villard.

Effect of bombardment by helium ions on critical currents of thin indium films

Abstract The critical currents of indium films irradiated by helium ions were measured. An effect of irradiation on j c ( H ⊥ ) characteristics was stated. This effect is due to the change of the degree of a disorder in a substance of the irradiated film.

Quasiperiodic superconducting V/Zr multilayers: critical magnetic fields and crossover

Critical magnetic fields parallel and perpendicular to the planes of quasiperiodic superconducting Fibonacci multilayers (ML) consisting of vanadium and zirconium are measured. The temperature dependence of the parallel critical field Hc∥ displays two crossovers. The Hc∥(T) dependence is of square-root type in the vicinity of the transition temperature Tc and linear at low temperatures. Between these temperature intervals, the dependence follows a power law: Hc∥∼(1−T/Tc)α, α=0,78±0,02. The complex nature of this dependence can be explained in the framework of the Ginzburg–Landau theory for a quasiperiodic ML, as well as by the scaling theory for fractal multilayers which takes into account the different structure length scales in the case of ML with a complex sequence of layers.

Ion implantation as a method of studying inhomogeneities in superconductors: Results for indium films with embedded helium particles

Abstract The paper considers the applicability of ion implantation into superconductors to investigate inhomogeneity effects on their macroscopic properties. Noble-gas-ion implantation into thin superconducting films is shown to be a unique means of systematically studying these effects in a single sample. Data demonstrating the effect of inhomogeneities on the critical current, I C , in the mixed state and phase-transition smearing in He+-ion-irradiated indium films are presented. First, experimental evidence was obtained to support the Larkin-Ovchinnikov theory which relates I C and the phase-transition smearing to inhomogeneities of the electron-electron interaction constant g(r) and the electron mean free path l(r) . Results are presented for parallel critical field anomalies in He-implanted indium films which are due to an implantation-induced anisotropy of ξ(t ). Changes in the critical parameters of the film resulting from the implantation are compared to structural changes.