7 research outputs found
Shapiro steps in Josephson junctions with alternating critical current density
We treat theoretically Shapiro steps in tunnel Josephson junctions with
spatially alternating critical current density. Explicit analytical formulas
for the width of the first integer (normal) and half-integer (anomalous)
Shapiro steps are derived for short junctions. We develop coarse-graining
approach, which describes Shapiro steps in the voltage-current curves of the
asymmetric grain boundaries in YBCO thin films and different
superconductor-ferromagnet-superconductor Josephson-type heterostructures.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev.
Single-vortex-induced voltage steps in Josephson-junction arrays
We have numerically and analytically studied ac+dc driven Josephson-junction
arrays with a single vortex or with a single vortex-antivortex pair present. We
find single-vortex steps in the voltage versus current characteristics (I-V) of
the array. They correspond microscopically to a single vortex phase-locked to
move a fixed number of plaquettes per period of the ac driving current. In
underdamped arrays we find vortex motion period doubling on the steps. We
observe subharmonic steps in both underdamped and overdamped arrays. We
successfully compare these results with a phenomenological model of vortex
motion with a nonlinear viscosity. The I-V of an array with a vortex-antivortex
pair displays fractional voltage steps. A possible connection of these results
to present day experiments is also discussed.Comment: 10 pages double sided with figures included in the text. To appear in
Journal of Physics, Condensed Matte
Mode-Locking in Driven Disordered Systems as a Boundary-Value Problem
We study mode-locking in disordered media as a boundary-value problem.
Focusing on the simplest class of mode-locking models which consists of a
single driven overdamped degree-of-freedom, we develop an analytical method to
obtain the shape of the Arnol'd tongues in the regime of low ac-driving
amplitude or high ac-driving frequency. The method is exact for a scalloped
pinning potential and easily adapted to other pinning potentials. It is
complementary to the analysis based on the well-known Shapiro's argument that
holds in the perturbative regime of large driving amplitudes or low driving
frequency, where the effect of pinning is weak.Comment: 6 pages, 7 figures, RevTeX, Submitte
Subharmonic steps in the I-V characteristic of short microbridges due to non-sinusoidal current-phase relations
The influence of high order harmonics (Ik sin kϕ, k > 1) of the current-phase relation I(ϕ) of a short superconducting microbridge on the corresponding rf-induced current-voltage characteristic is studied. For a special non-sinusoidal relation I(ϕ) derived from the model of Baratoff et al., the step-heights are calculated as function of the amplitude of the applied rf-field. An approximation method for the determination of the spectrum Ik of I(ϕ) by means of an evaluation of the given step-structure is discussed