Regensburg 2010 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 7: SC: Heterostructures, Andreev Scattering, Proximity Effect, Coexistence
TT 7.13: Vortrag
Montag, 22. März 2010, 17:30–17:45, H20
Spin-controlled supercurrents in quantum-dot spin valves with a superconducting lead — •Björn Sothmann1, David Futterer1, Michele Governale2, and Jürgen König1 — 1Universität Duisburg-Essen and CeNIDE, 47048 Duisburg, Germany — 2School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand
Quantum dots coupled to ferromagnetic [1] or superconducting [2] electrodes exhibit interesting effects due to an interplay of strong Coulomb interaction, superconducting proximity effect and nonequilibrium spin accumulation as well as spin precession.
Here we investigate a quantum-dot spin valve, i.e., a single-level quantum dot coupled to two ferromagnetic leads with symmetrically applied bias, with an additional superconducting lead at zero chemical potential. Using a real-time diagrammatic approach [1,2] we compute the current taking into account the coupling to the superconductor exactly in the limit of infinite pair potential. For a symmetric coupling to the ferromagnets, the current into the superconductor vanishes in collinear geometries due to a combination of particle-hole and left-right symmetry. A finite supercurrent arises only for noncollinear magnetizations in the intermediate bias regime due to a breaking of the left-right symmetry by the spin accumulation. Due to the presence of an exchange field, the supercurrent shows a nontrivial bias dependence and can even change sign.
[1] M. Braun, J. König, J. Martinek, Phys. Rev. B. 70 (2004).
[2] M. Governale, M. Pala, J. König, Phys. Rev. B. 77 (2008).