Since the ferromagnetic side of a superconductor-ferromagnet junction is spin polarized, Andreev reflections are suppressed. Consequently, the induced superconductor order parameter in the ferromagnet is expected to decay rapidly, on the order of a few nm. Our scanning tunneling spectroscopy measurements on thin epitaxial (100)YBa₂Cu₃O_7-δ-SrRuO₃ (YBCO-SRO) bilayers, where SRO is a ferromagnet, indeed show that on most of the junction area the superconductor order parameter vanishes in the SRO over a distance less than 8 nm. However, we find localized regions, arranged along narrow (<10 nm) stripes, where the order parameter (superconductor-like gap structure) penetrates the ferromagnet more than 20 nm. This is attributed to "crossed Andreev reflections", taking place at domain boundaries, where an electron from one magnetic domain is retro reflected as a hole with opposite spin in an adjacent domain. This phenomenon, directly observed here for the first time, may account for the (not abundant) cases where a long-range proximity effect was found in superconductor-ferromagnet proximity systems.

Date Published: 30 August 2005
PDF: 8 pages
Proc. SPIE 5932, Strongly Correlated Electron Materials: Physics and Nanoengineering, 593216 (30 August 2005); doi: 10.1117/12.621040

Published in SPIE Proceedings Vol. 5932:
Strongly Correlated Electron Materials: Physics and Nanoengineering
Ivan Bozovic; Davor Pavuna, Editor(s)