Condensed Matter Seminar

Norman O. Birge
Michigan State University

Tuesday, March 10, 2009; 4:00 pm in JFB 334

Josephson Junctions with Ferromagnets

Superconducting/Ferromagnetic (S/F) hybrid systems exhibit a number of interesting properties due to the interplay between the competing symmetries of their order parameters. With conventional spin-singlet superconductors, the proximity effect in S/F systems decays over an extremely short length scale in the ferromagnet due to the large exchange splitting between the spin-up and spin-down electron bands. In S/F/S Josephson junctions, the critical current oscillates and decays rapidly as a function of the ferromagnetic layer thickness. If there were spin-triplet pair correlations, however, both the proximity and Josephson effects would persist over much longer distances. Such correlations have been predicted to occur in S/F systems with certain forms of magnetic heterogeneity near the S/F interface [1]. In this talk I'll present our recent work on S/F/S Josephson junctions made with a variety of different F materials including both strong and weak ferromagnets, and I'll speculate on why we haven't yet found the elusive spin-triplet pair correlations.

[1] F.S. Bergeret, A.F. Volkov, and K.B. Efetov, Rev. Mod. Phys. 77, 1321 (2005).