Download Superconducting Spintronics: Superconductor/Ferromagnet

SUPERCONDUCTING SPINTRONICS:
Superconductor/Ferromagnet Structures with Spin-Orbit Coupling
Jabir Ali Ouassou¹, Jacob Linder¹
¹Department of Physics, Norwegian University of Science and Technology, Trondheim, Norway
In structures that consist of superconductors in conjunction with normal metals, superconducting
properties can also be induced over mesoscopic distances in the adjacent material, a phenomenon
known as the proximity effect. It turns out that if the normal metal has inherent magnetic properties,
the proximity coupling can give rise to a plethora of novel physical phenomena, which in recent
years has garnered a lot of interest from theorists and experimentalists alike. One particularly
striking effect, is that the presence of either (i) an inhomogeneous magnetic field or (ii) a spin-orbit
coupling can lead to long-range triplet generation (Bergeret et al., 2001 Phys. Rev. B 86 4096;
Bergeret & Tokatly, 2013 Phys. Rev. Lett. 110 117003). This constitutes a kind of superconductivity
carried by electron pairs in the triplet state |↑↑) or |↓↓), whereas conventional superconductivity is
restricted to pairs in the singlet state |↑↓) − |↓↑). Thus the generation and manipulation of spinpolarized supercurrents is made possible by superconductor/ferromagnet hybrid structures, an effect
that already has been realized in experiments (Keizer et al., 2006 Nature 439 825), and which could
possibly lead to new types of device functionality based on spintronics.
In this presentation, we will first provide a brief introduction to the superconductivity of such
hybrid structures, including the essential equations which are used in a quantitative treatment
of the matter. Then, we will present theoretical predictions for the effect of spin-orbit coupling on
superconductor/ferromagnet bilayers. This includes indications of a triplet spin-valve effect in such
bilayers, which means that the superconductivity throughout the structure can be switched on/off by
a π/2 rotation of the magnetic field orientation in the ferromagnet.
Keywords: Spintronics, Proximity Effect, Superconductivity, Ferromagnetism, Spin-Orbit Coupling.