Session H1: Spin-Triplet Supercurrents in Superconductor/Ferromagnet/Superconductor Josephson Junctions

8:00 AM–11:00 AM, Tuesday, March 22, 2011
Room: Ballroom A1

Sponsoring Unit: DCMP
Chair: James Sauls, Northwestern University

Abstract ID: BAPS.2011.MAR.H1.5

Abstract: H1.00005 : Long-ranged supercurrents through half-metallic ferromagnetic CrO$_2$

10:24 AM–11:00 AM

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  Jan Aarts
    (Leiden University)

In the last few years, the scenery in the physics of superconductor/ ferromagnet hybrids has changed considerably with the realization that spin triplets may be induced in the ferromagnet through the mechanism of odd-frequency pairing. Since the equal-spin component of the triplet is not susceptible to pair breaking by the exchange field, such correlations can sustain supercurrents over long lengths, in particular in fully spin polarized materials where only one spin band is available. In halfmetallic ferromagnetic CrO$_2$ for instance, where superconducting contacts were deposited on top of the ferromagnetic films, we observed the current to flow over 700~nm at 4.2~K [1]. Still, we also have fabricated devices where the supercurrent is absent, which indicates that the mechanism of triplet generation is not yet well in hand. The presence of non-homogeneous magnetization is important, and here the grain structure of the film appears to play a key role, as can be illustrated with data for films grown on different substrates (TiO$_2$ and Al$_2$O$_3$). Moreover, recent data will be presented which suggest that triplet generation can be improved by using an additional ferromagnetic layer in the contact area. \\ \newline [1] M. S. Anwar, F. Czeschka, M. Hesselberth, M. Porcu, and J. Aarts, Phys. Rev. B {\bf 82}, 100501(R) (2010).

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