Biomedical subjects

A Sterck

Publications and source records attributed to A Sterck.

4 recordsLinked to original sources

PubMed2006

Commensurability effects in superconducting Nb films with quasiperiodic pinning arrays.

We study experimentally the critical depinning current I(c) versus applied magnetic field B in Nb thin films which contain 2D arrays of circular antidots placed on the nodes of quasiperiodic (QP) fivefold Penrose lattices. Close to the transition temperature T(c) we observe matching of the vortex lattice with the QP pinning array, confirming essential features in the I(c)(B) patterns as predicted by Misko et al. [Phys. Rev. Lett. 95, 177007 (2005)]. We find a significant enhancement in I(c)(B) for QP pinning arrays in comparison to I(c) in samples with randomly distributed antidots or no antidots.

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PubMed2005

Three-junction SQUID rocking ratchet.

We investigate three-junction SQUIDs which show voltage rectification if biased with an ac current drive with zero mean value. The Josephson phase across the SQUID experiences an effective ratchet potential, and the device acts as an efficient rocking ratchet, as demonstrated experimentally for adiabatic and nonadiabatic drive frequencies. For high-frequency drives the rectified voltage is quantized due to synchronization of the phase dynamics with the external drive. The experimental data are in excellent agreement with numerical simulations including thermal fluctuations.

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PubMed2004

Dynamics of semifluxons in Nb long Josephson 0-pi junctions.

We propose, implement, and test experimentally long Josephson 0-pi junctions fabricated using conventional Nb-AlOx-Nb technology. We show that by using a pair of current injectors one can create an arbitrary discontinuity of the Josephson phase and, in particular, a pi discontinuity, just as in d-wave/s-wave or in d-wave/d-wave junctions, and study fractional Josephson vortices which spontaneously appear. Moreover, using such junctions, we can investigate the dynamics of the fractional vortices-a domain which is not yet available for natural 0-pi junctions due to their inherently high damping. We observe half-integer zero-field steps which appear on the current-voltage characteristics due to the hopping of semifluxons.

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PubMed2001

Josephson vortex in a ratchet potential: theory.

We propose a type of Josephson vortex ratchet. In this system a Josephson vortex moves in a periodic asymmetric potential under the action of a deterministic or random force with zero time average. For some implementations the amplitude of the potential can be controlled during the experiment, thus allowing us to tune the performance of the system and build rocking as well as flashing ratchets. We discuss the differences between conventional and Josephson vortex ratchets and present a model describing the dynamics of the fluxon in such a system. We show numerical simulation results that predict rectification of a monochromatic, deterministic signal with zero time average. The investigation of this system may lead to the development of the fluxon rectifier-a device that produces a dc voltage from nonequilibrium fluctuations.

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