FEMTOSECOND NEAR-FIELD SPIN MICROSCOPY IN DIGITAL MAGNETIC HETEROSTRUCTURES

We have designed a low-temperature femtosecond-resolved near-field sca nning optical microscope to study spatiotemporal excitonic spin behavi or in magnetic semiconductor heterostructures. Local disorder introduc ed by focused-ion-beam implantation reduces the otherwise large Zeeman splittings in modest magnetic fields, creating a planar spin-dependen t energy landscape for diffusing carriers. Near-field polarization-res olved static and femtosecond measurements map out excitonic spin behav ior with similar to 125 nm spatial resolution, revealing spin-dependen t diffusion. We demonstrate the applicability of two distinct time res olved techniques in the near held, and discuss Limitations on the meas urement of polarized luminescence from semiconductors in the near fiel d. (C) 1996 American Institute of Physics.