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TT: Fachverband Tiefe Temperaturen
TT 15: Superconductivity - Tunneling, Josephson Junctions, SQUIDs
TT 15.3: Talk
Tuesday, March 27, 2007, 14:30–14:45, H20
Unusual Properties of High–Tc SQUIDs — •Christof Schneider1, Florian Loder1, Thilo Kopp1, John Kirtley2, Helene Raffy3, and Jochen Mannhart1 — 1Lehrstuhl für Experimentalphysik VI, Institut für Physik, Universität Augsburg, D-86135 Augsburg — 2IBM Thomas J. Watson Research Center, P.O.Box 218, Yorktown Heights, New York 10598, USA — 3Laboratoire de Physique des Solides, Université de Paris-Sud, 91405 Orsay, France
Current-voltage characteristics of SQUIDs show a periodic variation of the critical current as a function of the applied magnetic field. Usually, the periodicity corresponds to one flux quantum Φ0 = h/2e. Low-inductance high–Tc grain boundary SQUIDs with a 0∘/45∘ misorientation however, display systematically a characteristic periodicity of the critical current of 1/2 × Φ0 in small magnetic fields. In this contribution we present a systematic study of high–Tc SQUIDs with different grain boundary misorientation angles. For most misorientations, critical current oscillations with periods of 1/2 × Φ0 in small magnetic fields have been identified. SQUIDs prepared on 24∘ and 30∘ bicrystalline substrates show highly unusual and complex diffraction patterns. The interpretation of the phase–sensitive experiments is only partly consistent with higher harmonics of the current–phase relation for the Josephson current.