APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011;
Dallas, Texas
Abstract: H1.00004 : Triplet supercurrents in ferromagnets
9:48 AM–10:24 AM
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In almost all superconductors the pairs of electrons which carry
the charge are in the so-called singlet state in which the
quantum spin of the two electrons is antiparallel. During the
past five years there has been increasing evidence that proximity
coupling between singlet superconductors and ferromagnets can
sometimes generate triplet pairs within the ferromagnet in which
the spins of the electrons are parallel rather than antiparallel
-- the evidence being that supercurrents can be passed through
thicknesses of ferromagnetic material which are simply too large
for singlet pairs to
survive.
The superconductor-ferromagnet proximity effect describes the
fast decay of a spin-singlet supercurrent originating from the
superconductor upon entering the neighboring ferromagnet. For
strong ferromagnets such as Co, a thickness of only a few
nanometres is sufficient to almost completely suppress the
critical current of a Nb/Co/Nb Josephson junction. Here we
report experiments in which a conical magnet (holmium) is placed
at the interface between the superconductor and ferromagnet. The
results showed that a long-ranged supercurrent can occur through
the ferromagnetic Co layer but only for certain critical
thicknesses of the Ho [1]. These thicknesses correspond to
maximum magnetic inhomogeneity on the Ho and are therefore
consistent with models which predict that a spin-mixing interface
between the superconductor and ferromagnet can generate triplet
pairs which are long-ranged in the ferromagnet.
This paper reports recent experiments which aim to understand
further the behaviour of triplet pairs in superconductor /
ferromagnet heterostructures.
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[1] J. W. A. Robinson, J. D. S. Witt, and M. G. Blamire,
``Controlled Injection of Spin-Triplet Supercurrents into a
Strong Ferromagnet'' Science \textbf{329}, 59-61 (2010).
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.H1.4