Regensburg 2000 – scientific programme

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TT: Tiefe Temperaturen

TT 6: Josephson-Kontakte und SQUIDs I

TT 6.2: Talk

Monday, March 27, 2000, 16:30–16:45, H19

π-state in ferromagnetic Josephson weak links — •Tero Heikkilä¹, Frank Wilhelm^1,2, and Gerd Schön¹ — ¹Institut für Theoretische Festkörperphysik, Universität Karlsruhe, 76128 Karlsruhe — ²Quantum Transport Group, TU Delft, 2600 GA Delft, The Netherlands

We examine theoretically the supercurrent in superconductor - weak ferromagnet - superconductor (SFS) sandwich structures. For certain strengths of the exchange field, these structures have been predicted to exhibit a π-state, where the supercurrent direction is opposite to the phase gradient. We develop a description within the quasiclassical technique in the diffusive limit and discuss the dependence of the π-current on temperature, energy gap of the superconductor, and the exchange field in the ferromagnet. For disordered phase coherent weak links with a diffusion constant D, all these scales can also be tuned by changing the width L of the link, and through it the Thouless energy E_T=ℏ D/L². The ratio between the other energy scales and E_T determine the properties of these structures.

We propose a way to observe this state directly and discuss the possible experimental configurations. These configurations may allow to study the interplay of the proximity effect with ferromagnetism in a single sample, hence avoiding the technological difficulty of fabricating a big number of reproducible samples with different geometric lengths, which was necessary in previously proposed scenarios.