Dynamics study of few-electron zero-dimensional spin system

在这个项目中，我们开发了新型的半导体纳米结构，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。主要研究内容有：1.量子点中少数电子的相互作用和2.量子点中的电子-核自旋耦合。1.我们研制了一种新型的耦合量子点-量子线器件，并以量子线为自旋选择接触引线，在填充因子为2-4的范围内，演示了电子通过量子点的自旋过滤效应。为了研究这种隧穿中的自旋稳健性，我们制备了一个带有静电耦合量子点的量子点，并使用量子点接触作为电荷探测器直接测量了自旋弛豫时间，并将得到的驰豫时间分配给了自旋-轨道相互作用的影响。我们发展了一种新的电泵浦-探测技术来测量垂直耦合双量子点的自旋弛豫时间，发现测量的驰豫时间受超精细耦合到核自旋的影响很大。我们开启了具有纳米间隙电极的InAs自组装量子点输运性质的新课题，首次在自组装量子点体系中发现了近藤效应，并讨论了自旋-轨道相互作用的影响。2.首次成功地对双量子点中的超精细耦合进行了电磁控制，获得了~50%的高核极化。我们还应用这一技术导出了以两个量子点能级之间的失谐为参数的交换耦合能，并证明了交换耦合相对于失谐量的稳定区域的存在。在获得电子自旋-核自旋耦合的基础上，利用核磁共振技术，我们首先演示了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.