Spatiotemporal near-field spin microscopy in patterned magnetic heterostructures.

Low temperature femtosecond-resolved near-field scanning optical microscopy is used to image excitonic spin behavior in locally disordered magnetic semiconductor heterostructures. A contrast between luminescence intensity and polarization profiles yields marked differences between carrier diffusion and spin transport over a spin-dependent energy landscape sharply defined by focused ion beam implantation. Space-time spectroscopies reveal a spin component to the exciton evolution in the presence of a magnetic field. Fundamental limitations on the measurement of circularly polarized luminescence in the near field are also demonstrated.