Dynamics study of few-electron zero-dimensional spin system

在这个项目中，我们开发了新的半导体纳米结构，并探索了限制在纳米结构中的零维电子相互作用的动力学。本文主要研究的课题有：1。2.量子点中少电子的相互作用。量子点中的电子-原子核自旋耦合。我们新开发了耦合量子点-量子线器件，并利用量子线作为自旋选择性接触引线，演示了电子在填充因子2 ~ 4范围内穿过量子点的自旋滤波效应。为了研究这种隧穿过程中的自旋鲁棒性，我们制备了一个具有静电耦合量子点的量子点，并利用量子点接触作为电荷探测器直接测量自旋弛豫时间，并将由此得到的弛豫时间分配给自旋轨道相互作用的影响。我们开发了一种新的电泵-探针技术来测量垂直耦合双量子点的自旋弛豫时间，并发现测量的弛豫时间受到核自旋超精细耦合的显著影响。我们开启了一个关于纳米间隙电极的InAs自组装量子点输运性质的新课题，首次在自组装量子点系统中发现了近田效应，并讨论了自旋轨道相互作用的影响，认为该InAs系统中自旋轨道相互作用很强。我们首次成功地在电和磁两方面控制了双量子点的超精细耦合，并实现了~50%的高度核极化。我们还应用该技术推导出了两个量子点能级间具有失谐的交换耦合能量作为参数，并证明了失谐的交换耦合稳定区域的存在。利用在此获得的电子自旋-核自旋耦合的知识，并使用核磁共振技术，我们首次证明了在量子点中核自旋的相干操纵。

In this project we have developed novel semiconductor nanostructures and explored dynamics of interacting zero-dimensional electrons confined to the nanostructures. The main topics study here are 1. Interaction of few-electrons in quantum dots and 2. Electron-nuclei spin coupling in quantum dots.1.We newly developed coupled quantum dot-quantum wire devices and demonstrated the spin-filtering effect for electrons tunneling through the dot in the regime of filling factor between 2 and 4, using the quantum wire as a spin-selective contact lead. To study the spin robustness in this tunneling we prepared a quantum dot with an electrostatically coupled quantum point and used the quantum point contact as a charge detector to directly measure the spin relaxation time, and assigned thus obtained relaxation time to the effect of spin-orbit interaction. We developed a new electrical pump-probe technique to measure spin relaxation time for vertically coupled double quantum dot and found that the measured relaxation time was significantly affected by hyperfine coupling to nuclear spin. We started a new topic about transport properties of an InAs self-assembled quantum dot with nano-gap electrodes, and found the Kondo effect for the first time in system of self-assembled quantum dots and discussed the effect of spin-orbit interaction, which is assumed to be strong in this InAs system.2.We first succeeded in both electrically and magnetically controlling the hyperfine coupling in a double quantum dot and achieved a high degree of nuclear polarization of ~50%. We also applied this technique to derive an exchange coupling energy with detuning between two quantum dot levels as a parameter, and demonstrated existence of stable region of exchange coupling with respect to the detuning. With the knowledge of electron spin-nuclear spin coupling obtained here and using an NMR technique, we first demonstrated coherent manipulation of nuclear spin in quantum dots.