Breakdown of the Korringa law of nuclear spin relaxation in metallic GaAs.

We present nuclear spin relaxation measurements in GaAs epilayers using a new pump-probe technique in all-electrical, lateral spin-valve devices. The measured T(1) times agree very well with NMR data available for T>1 K. However, the nuclear spin relaxation rate clearly deviates from the well-established Korringa law expected in metallic samples and follows a sublinear temperature dependence T(1)(-1) is proportional to T(0.6) for 0.1 K≤T≤10 K. Further, we investigate nuclear spin inhomogeneities.

Scanning tunneling microscope excited cathodoluminescence from ZnS nanowires.

The electronic excitation spectrum of ZnS nanowires (NWs) is characterized by cathodoluminescence (CL) excited using the tip of a scanning tunneling microscope as a highly localized and bright source of low-energy (150-350 eV) electrons with impinging power densities in the range of up to 60 kW/cm(2) or more. The CL spectra reveal significant differences when compared with the photoluminescence spectra of ZnS NWs. The differences can be associated with the properties of the surface region of the NWs, which are preferentially emphasized in the CL spectra owing to the small probing depth of low-energy electrons.