Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 11: Superconductivity: Heterostructures, Andreev Scattering, Proximity Effect, Coexistence
TT 11.3: Vortrag
Dienstag, 28. März 2006, 10:00–10:15, HSZ 301
Triplet supercurrent through a half-metallic ferromagnet — •S. T. B. Goennenwein1,2, R. S. Keizer2, T. M. Klapwijk2, G. Miao3,4, G. Xiao4, and A. Gupta3 — 1Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching, Germany — 2Kavli Insitute of NanoScience, Faculty of Applied Sciences, Delft University of Technology, Delft, The Netherlands — 3MINT Center, University of Alabama, Tuscaloosa, USA — 4Physics Department, Brown University, Providence, USA
Superconductivity and ferromagnetism usually do not coexist, as the Cooper pairs in conventional superconductors are spin singlets (pairs of electrons with antiparallel spin), while the ferromagnetic exchange interaction requires parallel spins. However, the existence of long-range superconducting triplet correlations in a ferromagnet in proximity to a conventional superconductor has been suggested.
Using electron-beam lithography, sputtering, and lift-off, we have patterned two NbTiN electrodes on top of a thin CrO2 film. We find that a Josephson supercurrent flows through this weak link for electrode separations of up to 1 µ m at T=1.7 K. The magnitude of the supercurrent oscillates as a function of the strength of an externally applied magnetic field (Fraunhofer pattern), and characteristically depends on the magnetization orientation in the CrO2 layer. We interpret these findings as evidence for a spin triplet supercurrent in the half-metallic ferromagnet CrO2, and discuss possible mechanisms for the singlet to triplet conversion at the superconductor-ferromagnet interface.