Nano-optical spin electronics based on near-field optical microscopic technique

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As well as the control of interband-polarization coherence, the storage and manipulation of spin coherence is of great importance in spintronics. The quantum confinement of electrons is advantageous for spintronics in terms of the control of spin behavior through the optimization of spin lifetime and g-factor. For local injection, control, and detection of spin-polarized electrons in individual quantum structures, optical spin manipulation with the near-field light source is needed.We have established a near-field scanning optical microscope (NSOM) system to measure and manipulate the spin state of a single quantum dot (QD) with a high spatiotemporal resolution under a magnetic field up to 5T. The spatial resolution as high as 30-50 nm enabled us to visualize wave functions of quantum-confined excitons.Owing to the high spatial resolution of our NSOM, the shape of the QD is clearly visualized. From magneto-PL spectroscopy of a single QD, a diamagnetic shift of the exciton emission was observed. Referring to the theoretical value we estimate the size of the QD from a diamagnetic coefficient, which is determined by the Bohr radius of excitons confined in QDs. The result was in good agreement with that obtained by the real-space NSOM mapping.We also built a near-field optical microscope for polarization spectroscopy in the reflection configuration. Polarization properties of good quality and stability as well as high optical throughput allows high-sensitive magneto-optical spectroscopy with high spatial resolution. Kerr-rotation imaging of magnetic domains in garnet thin films and depolarization microscopy of a phase-change material with a spatial resolution of 30 nm are demonstrated.