Source: thznetwork.org

    An electron spin-dependent plasmonic transport effect at terahertz frequencies has been demonstrated by a team of researchers from the University of Alberta (Edmonton, Canada) and the Naval Research Laboratory (Washington, D. C., U.S.A.). In their experiments, spintronic structures consisting of sub-wavelength size ferromagnetic particles coated with nonmagnetic nano-layers are excited with a single-cycle, terahertz electric field pulse. The incident electric field induces nonresonant particle plasmons on the surface of the individual ferromagnetic/nonmagnetic composite particles. The dipolar electric fields associated with the particle plasmons couple between closely spaced particles via nearest neighbor interaction and coherently radiate into the far-field at the edge of the sample. When a magnetic field is applied to the spintronic medium, electron spin induced resistivity changes within the skin depth of the particles are mapped onto a modulation of the radiated electromagnetic fields. Remarkably, terahertz radiation propagated through the spintronic ferromagnetic/nonmagnetic structures shows dramatically increased magnetically dependent attenuation relative to that of structures consisting of purely ferromagnetic or nonmagnetic particles. The mechanism causing the striking enhancement of the magnetically induced attenuation arises from non-equilibrium accumulation of electron spin electromagnetically driven from the ferromagnet into the nonmagnetic layer. Detailed studies of the dependence of the attenuation on the thickness of the nonmagnet layer is in very good agreement with the spin diffusion length predicted by the spin accumulation model and agrees with other experimental measurements of this length scale. The demonstration of spin-dependent plasmonic propagation offers in new degree of freedom in the design of next-generation photonics devices. Furthermore, there is good evidence that this spin-dependent effect is non-volatile, such that modulation can occur without the further application of power. The work appears in the article by K. J. Chau, Mark Johnson, and A. Y. Elezzabi ¡°Electron-Spin-Dependent Terahertz Light Transport in Spintronic-Plasmonic Media,¡± Physical Review Letters 98, 133901 (2007).

 
    Conceptual illustration (above) of a nonresonant particle plasmon excited on a spintronic structure consisting of a sub-wavelength size ferromagnetic (Co) particle that has been coated with nonmagnetic (Au) layers. Shown below are the density of spin-up and spin-down electron states, N(E), in the ferromagnetic and nonmagnetic media. In an applied magnetic field, spin polarized electrons in the ferromagnet are electromagnetically driven into the nonmagnet layer, which results in excess interface resistance. The electron-spin induced resistivity change is mapped onto a modulation of the fields re-radiated from the non-resonant particle plasmon.