Condensed Matter Seminar Series

Spin-Triplet Supercurrent in Ferromagnetic Josephson Junctions

Norman O. Birge

Michigan State University

Thursday September 22,  11:30 am,  Room 298,  Physics Building

Abstract:  When a superconductor (S) and a ferromagnet (F) are put into contact with each other, interesting things happen, and the combined S/F hybrid system exhibits altogether new properties.  There is a proximity effect where pair correlations from S penetrate into F, but this proximity effect decays over a very short distance due to the large energy splitting between the spin-up and spin-down electrons.  Theory predicts that, under certain conditions, electron pair correlations will appear with spin-triplet rather than spin-singlet symmetry [1].  The two electrons in such a spin-triplet pair have parallel spins and are not energy split in F; hence they propagate long distances.  Furthermore, these triplet correlations satisfy the Pauli Exclusion Principle in a new and strange way: they are odd in frequency or time.  In this talk I will discuss our recent observation of these pair correlations in experiments with S/F/S Josephson junctions [2].

[1] F.S. Bergeret, A.F. Volkov, and K.B. Efetov, Rev. Mod. Phys. 77, 1321 (2005).
[2] T.S. Khaire, M.A. Khasawneh, W.P. Pratt, Jr., N.O. Birge, Phys. Rev. Lett. 104, 137002 (2010).