Regensburg 2007 – scientific programme

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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–T_c 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–T_c 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–T_c 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.