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TT: Tiefe Temperaturen

TT 10: Superconductivity - Tunneling, Josephson Junctions, SQUIDs

TT 10.1: Vortrag

Samstag, 5. März 2005, 08:30–08:45, TU H104

High–T_c SQUIDs With an Unusual Current–Phase Relation — •Christof Schneider¹, German Hammerl², Gennadij Logvenov¹, Thilo Kopp¹, John Kirtley³, Peter Hirschfeld⁴, Helene Raffy⁵ und Jochen Mannhart¹ — ¹Lehrstuhl für Experimentalphysik VI, Institut für Physik, Universität Augsburg, D-86135 Augsburg — ²IBM Zurich Research Laboratory, CH 8803 Rueschlikon, Switzerland — ³IBM Thomas J. Watson Research Center, P.O.Box 218, Yorktown Heights, New York 10598, USA — ⁴Department of Physics, University of Florida, Gainesville, Florida 32611, USA — ⁵Laboratoire de Physique des Solides, Université de Paris-Sud, 91405 Orsay, France

Current-voltage characteristics of SQUIDs show as a function of the applied magnetic field a periodic variation of the critical current. Usually, the periodicity corresponds to one flux quantum Φ₀ = h/2e. In this contribution we present measurements of high–T_c SQUIDs showing a characteristic periodicity of the critical current of 1/2 × Φ₀ in small magnetic fields. The interpretation of the phase–sensitive experiments is consistent with higher harmonics of the current–phase relation for the Josephson current. They are also consistent with a finite interaction between Cooper pairs, leading to a quartet formation of electrons as a possible admixture to the superconducting condensate.