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DY: Dynamik und Statistische Physik

DY 50: Gitter- und Spindynamik

DY 50.1: Vortrag

Freitag, 26. März 1999, 09:30–09:45, R4

Experiments with Josephson ladders — •Peter Binder, Pasqualina Caputo, and Alexey V. Ustinov — Physikalisches Institut III, Universität Erlangen-Nürnberg, Erwin-Rommel-Straße 1, D-91058 Erlangen

We experimentally investigate a novel highly-discrete nonlinear lattice called Josephson ladder. A ladder is formed by two 1D chains of small Josephson junctions (called horizontal junctions) mutually coupled by another set of junctions (called vertical junctions). The elementary cell of the ladder contains 4 Josephson junctions. The anisotropy of Josephson coupling in the horizontal and vertical directions determines the discreteness of the system and leads to interesting physical effects.

Every vertical junction in our experiment is biased with a dc current. The current at which the ladder jumps from the superconducting (static) state to the normal (dynamic) state is called the critical current. We present systematic experimental data of the critical current dependence on the frustration induced by the external magnetic field. The obtained results clearly differ from that of a 1D parallel Josephson junction array which is well described by the discrete sine-Gordon model.

When locally injecting a current into the ladder, the excitation of a novel mode called discrete roto-breather [1] is expected. Such breather should be temporally stable and remain spatially localized. Measurements which attempt to observe these excitations will be reported.

[1] L. M. Floria, J. L. Marín, S. Aubry, P. J. Martínez, F. Falo, and J. J. Mazo, Physica D 113, 387 (1998).