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CAMP Seminar: Spin-triplet supercurrent in ferromagnetic Josephson junctions

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Norman O. Birge, Michigan State University
25 February 2014 from 3:30 PM to 4:30 PM
339 Davey Laboratory
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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 observation of these pair correlations in experiments with S/F/S Josephson junctions [2]. At the end of the talk, I’ll discuss future prospects for using such junctions as elements in a superconducting memory.


[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); C. Klose et al., Phys. Rev. Lett. 108, 127002 (2012).