Femtosecond near-field spin microscopy in digital magnetic heterostructures (invited)

We have designed a low-temperature femtosecond-resolved near-field scanning optical microscope to study spatiotemporal excitonic spin behavior in magnetic semiconductor heterostructures. Local disorder introduced by focused-ion-beam implantation reduces the otherwise large Zeeman splittings in modest magnetic fields, creating a planar spin-dependent energy landscape for diffusing carriers. Near-field polarization-resolved static and femtosecond measurements map out excitonic spin behavior with ∼125 nm spatial resolution, revealing spin-dependent diffusion. We demonstrate the applicability of two distinct time-resolved techniques in the near field, and discuss limitations on the measurement of polarized luminescence from semiconductors in the near field.