Spatiotemporal near-field spin microscopy in digital magnetic heterostructures

A femtosecond-resolved low-temperature near-field scanning optical microscope (NSOM) is used to monitor the spatiotemporal evolution of excitonic spins in magnetic semiconductor quantum structures which are laterally patterned with a focused beam of Ga⁺ ions. Polarization-resolved photoluminescence (PL) images reveal a spin-dependent energy landscape in which the Zeeman splitting is diminished in implanted regions, and carrier and spin behavior directly distinguished by sharp differences in intensity and polarization profiles. Time-resolved measurements suggest that exciton diffusion acquires a spin-dependent component in the presence of a magnetic field. The data demonstrates fundamental limitations on the measurement of polarized PL from semiconductors in the near-field regime, and exhibits distinct differences between near-field detection and near-field excitation of emitted PL. The heterostructures consist of single 120 Å ZnSe/ZnCdSe MBE-grown semiconductor quantum wells (QW) containing a systematic distribution of magnetic ions (Mn²⁺). In magnetic fields, traditional magneto-optical data show narrow PL linewidths and large Zeeman splittings, making them ideal systems in which to study local spin-dependent interactions