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

除了控制带间偏振相干性外，自旋相干性的存储和操纵在自旋电子学中也是非常重要的。电子的量子限制有利于自旋电子学通过优化自旋寿命和g因子来控制自旋行为。为了对单个量子结构中的自旋极化电子进行局域注入、控制和检测，需要利用近场光源进行光学自旋操控。我们建立了一套近场扫描光学显微镜(NSOM)系统，用于测量和操控单个量子点(QD)在高达5T磁场下的自旋态。高达30-50 nm的空间分辨率使我们能够可视化量子受限激子的波函数，由于我们的非自组织光学显微镜的高空间分辨率，量子点的形状被清晰地可视化。从单个量子点的磁致发光光谱中观察到激子发射的反磁位移。参照理论值，我们从一个由限制在量子点中的激子的玻尔半径决定的抗磁系数来估计量子点的大小。实验结果与实空间NSOM映射的结果吻合较好。我们还搭建了一台近场光学显微镜，用于反射结构的偏振光谱。高质量和稳定性的偏振特性以及高的光学吞吐量使得高灵敏度的磁光光谱具有高的空间分辨率。对石榴石薄膜的磁畴进行了克尔旋转成像，并对空间分辨率为30 nm的相变材料进行了退偏显微镜观察。

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.