Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 19: Supraleitung: Heterostrukturen, Andreev-Streuung, Proximity-Effekt, Koexistenz
TT 19.4: Vortrag
Mittwoch, 10. März 2004, 17:45–18:00, H20
Spontaneous Current in a Superconducting Loop with Ferromagnetic Josephson Junction — •Andreas Bauer1, Johannes Bentner1, Marco Aprili2,3, Maria-Luisa Della Rocca2,3, Matthias Reinwald1, Werner Wegscheider1, and Christoph Strunk1 — 1Institut für Experimentelle und Angewandt Physik, Universität Regensburg, Germany — 2CSNSM-CNRS, Université Paris-Sud, Orsay, France — 3LPQ-ESPCI, 75005 Paris, France
Recently it has been shown that Cooper pairs can be transferred coherently across a very thin ferromagnetic interlayer sandwiched between two superconducting reservoirs. Thereby an exchange field acts upon the spins of the paired electrons, resulting in a spatially oscillating pair amplitude. For proper values of the ferromagnetic layer thickness and exchange field, this oscillation allows the construction of Josephson-junctions with a built-in phase difference of π. Niobium loops interrupted by a PdNi π-junction are fabricated by means of shadow evaporation using a high temperature stable shadow mask made of Polyethersulfone and Germanium. A single loop is placed on top of the active area of a micro-Hall sensor made of a modulation doped GaAs/AlGaAs heterostructure. By varying the applied magnetic field, the phase difference across the weak link is tuned. When comparing the magnetic response of loops with and without π-junction, the π-loop is found to be asymmetric when reversing the applied magnetic field. Upon cooling down the loop below the critical temperature in zero field, a spontaneous current is detected which provides half-integer flux quantization in the π-loop. Both effects can be understood in terms of the intrinsic phase bias of the π-junction.