Justin Watts

Self-Assembled ErSb Nanostructures with Optical Applications in Infrared and Terahertz

Plasmonic effects have proven to be very efficient in coupling light to structures much smaller than its wavelength. Efficient coupling is particularly important for the infrared or terahertz (λ ∼ 0.3 mm) region where semiconductor structures and devices may be orders of magnitude smaller than the wavelength and this can be achieved through nanostructures that have a desired plasmonic response. We report and demonstrate a self-assembly method of embedding controllable semimetallic nanostructures in a semiconducting matrix in a ErSb/GaSb material system grown by molecular beam epitaxy. The plasmonic properties of the ErSb/GaSb are characterized and quantified by three polarization-resolved spectroscopy techniques, spanning more than 3 orders of magnitude in frequency from 100 GHz up to 300 THz. Surface plasmons cause the semimetallic nanostructures to resonate near 100 THz (3 μm wavelength), indicating the semimetal as a potential infrared plasmonic material. The highly conductive ErSb nanowires polarize electromagnetic radiation in a broad range from 0.2 up to ∼100 THz, providing a new platform for electromagnetics in the infrared and terahertz frequency ranges.

Room temperature spin Kondo effect and intermixing in Co/Cu non-local spin valves

The anomalous low temperature suppression of the spin accumulation signal Δ R N L in non-local spin valves (NLSVs) based on common ferromagnet (FM)/normal metal (N) pairings has recently been shown to result from a manifestation of the Kondo effect. Local magnetic moments in the N due to even minor levels of FM/N interdiffusion depolarize the injected spin current, suppressing the effective spin polarization around and below the Kondo temperature T K . Previous studies have focused on FM/N combinations that happen to have low T K so that Kondo effects occur only well below 300 K. Here, we study NLSVs based on Co/Cu, a materials combination that is not only technologically relevant but also has a high T K , up to 500 K. Despite the negligible equilibrium solubility of Co in Cu, we find clear Kondo effects in both Δ R N L and Cu resistivity, due to Co/Cu intermixing that we probe via quantitative transmission electron microscopy. Most significantly, under certain conditions the spin Kondo effect suppresses ...