Josephson junctions using a strong ferromagnetic interlayer and spin triplet superconductivity

by Khasawneh, Mazin Alaya, Ph.D., MICHIGAN STATE UNIVERSITY, 2010, 137 pages; 3458522

Abstract:

Superconductivity and ferromagnetism are two competing phenomena: a superconductor expels a magnetic field, which in turn tries to weaken the superconductivity. However, the coexistence of conventional spin singlet (two electrons of opposite spin) superconductivity, and ferromagnetism (electron spins are aligned parallel) may be achieved by fabricating superconductor/ferromagnet (S/F) hybrid structures. The interplay between conventional superconductivity and magnetism in S/F systems leads to a fast decay of the order parameter in the F-layer as the two electrons from the spin-singlet Cooper pair enter different spin bands and rapidly lose phase coherence. It has been predicted that spin triplet pair correlations can be created near the S/F interface in the presence of certain kinds of magnetic inhomogeneity. If the spin triplet correlations are present at the SF interface, then the spin triplet proximity effect persists over much longer distances in the ferromagnet. These correlations exhibit a new type of symmetry: they are odd in frequency or time. The essence of this project was a systematic approach to observe these correlations in Co-based Josephson junctions. Since our early data didn't show any sign of long-range spin triplet correlations, we decided to split the observation process into two stages: generation and propagation. Generation of spin triplet correlations at the SF interface is provided by a thin layer of Cu0.48 Ni0.52 alloy placed next to the Nb electrodes. For the propagation, we used a Synthetic Antiferromagnet, SAF configuration consisting of Co(x)/Ru(0 6 nm)/Co(x) as thick as 2x = 39 nm. We observed a large enhancement in the supercurrent compared to junctions without the CuNi alloy. These experimental observations provide strong evidence for the long triplet nature of these correlations.

AdviserNorman O. Birge
SchoolMICHIGAN STATE UNIVERSITY
Source TypeDissertation
SubjectsElectromagnetics; Condensed matter physics
Publication Number3458522

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