ECRYS - 93
J. Phys. IV France 03 (1993) C2-79-C2-82
AC response of Abrikosov vortices in layered superconductorsS.N. ARTEMENKO1, C. KRÄMER2 and W. WONNEBERGER2
1 Institute of Radioengineering & Electronics of the Russian Academy of Sciences, Mokhovaya 11, 103907 Moscow, Russia
2 Department of Physics, University of Ulm, 7900 Ulm, Germany
In a layered high-Tc superconductor an Abrikosov vortex line perpendicular to the layers can be considered as a stack of coupled two-dimensional "pancake" vortices (2DV) with cores residing inside the superconducting layers . When the in-plane penetration length λab = λ is smaller than the Josephson length λj = λdd/λ (d : layer period) the interaction between 2DV is via a magnetic pair force which is complicated but exactly known. We calculate linear and nonlinear ac responses for this model including randomly distributed pinning centers. In detail, the thermally averaged shift Sn(t) of a 2DV in layer n under the influence of a finite external ac curreut in the frequency range up to 1 GHz is computed from coupled Fokker-Planck equations for the distribution functions of 2DV positions. In the adiabatic approximation, the Fokker-Planck equatious can be cast into a nonlinear differential equation for a continuous shift function S(z,t) using a gradient expansion. The constitutive equation for S(z,t) is solved perturbatively for the linear ac response and for the mixing current at frequency 2ω1 - ω2 from two external currents at frequencies ω1 and ω2 ≈ 2ω1 due to a third order process. This pseudo-harmonic mixing probes the nonlinearity of the intervortex force and its interplay with pinning. Explicit results for the film geometry are given for the surface impedance Z0 and the rnixing current amplitude δj(3) as functions of external frequencies, crossover frequency ωc α nidωD (measuring the pinning), and diffusion frequency ωD of free 2DV.
© EDP Sciences 1993