SQUID ratchets: basics and experiments |
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Authors: | A Sterck S Weiss D Koelle |
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Institution: | Universit?t Tübingen, Physikalisches Institut, Experimentalphysik II, auf der Morgenstelle 14, 72076 Tübingen, Germany, DE Universit?t zu K?ln, II. Physikalisches Institut, Angewandte Physik, Zülpicherstr. 77, 50937 K?ln, Germany, DE
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Abstract: | Superconducting quantum interference devices (SQUIDs) are very well suited for experimental investigations of ratchet effects.
This is due to the periodicity of the Josephson coupling energy with respect to the phase difference δ of the superconducting
macroscopic wave function across a Josephson junction. We show first that, within the resistively and capacitively shunted
junction model, the equation of motion for δ is equivalent to the motion of a particle in the so-called tilted washboard potential,
and we derive the conditions which have to be satisfied to build a ratchet potential based on asymmetric dc SQUIDs. We then
present results from numerical simulations and experimental investigations of dc SQUID ratchets with critical-current asymmetry
under harmonic excitation (periodically rocking ratchets). We discuss the impact of important properties like damping or thermal
noise on the operation of SQUID ratchets in various regimes, such as adiabatically slow or fast nonadiabatic excitation.
Received: 22 November 2001 / Accepted: 14 January 2002 / Published online: 22 April 2002 |
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Keywords: | PACS: 05 60 -k 05 40 -a 85 25 Dq |
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