QQ客服 官方微博 反馈留言

题名	纳米半导体电子自旋超快光学调控中若干重要问题研究
作者	李霞
学位类别	博士
答辩日期	2012
授予单位	中国科学院上海光学精密机械研究所
导师	徐至展
关键词	自旋相干性，II-VI族半导体量子点，时间分辨法拉第旋转光谱，飞秒激光，纳米周期阵列结构
其他题名	Study on several important issues of ultrafast optical manipulation of electron spins in semiconductor nanostructures
中文摘要	纳米半导体的电子自旋有望于实现固态量子信息处理，重要的前提条件是：具有长退相干时间、实现快速的量子操作以及量子比特的可拓展化。而实际器件化还需要在室温条件下满足以上前提。针对这些要求，本论文重点研究了若干II-VI族半导体胶体量子点的电子自旋超快动力学以及相干操控。考虑到胶体量子点结构比较单一且为无序堆集，我们通过飞秒激光干涉技术制备了多种有序的纳米周期阵列结构，有望为自旋电子学特别是自旋量子比特的可拓展性问题提供新的研究思路。 具体研究内容以及所获得的主要创新性结果归纳如下： （1） 在室温下利用时间分辨的法拉第旋转光谱技术首次系统研究了CdS胶体量子点的自旋退相干动力学，发现其电子自旋退相干时间可长达3 ns以上。根据自旋退相干时间随磁场依赖关系，可推测低磁场下自旋退相干主要因素为电子自旋-核自旋超精细耦合相互作用，而在较高磁场下，则由量子点非均匀展宽决定。另外CdSe量子点的自旋研究中也发现有类似的退相干机制。 （2） 室温下研究了CdTe单核量子点和CdTe/CdS II型核壳结构量子点的载流子以及自旋动力学，结果表明：II型核壳结构由于电子-空穴的空间有效分离，从而具有比单核量子点更长的载流子激发和弛豫时间，且随壳层厚度的增加逐渐增长；对于CdTe单核或CdTe/CdS核壳结构量子点，在外磁场下均无明显的自旋旋进信号，仅观测到单调衰减的非旋进自旋弛豫过程。 （3） 首次在室温下利用飞秒激光脉冲研究了量子点自旋相干态的超快旋转操控。由于所使用的800 nm控制波长远偏离CdSe量子点的共振波长（约600 nm），仅获得了初步的调制信号。尽管如此，仍可看出利用光stark效应已可实现室温下亚皮秒量级的电子自旋超快相干旋转控制。 （4） 在飞秒激光多光束干涉技术的基础上，通过改变激光强度以及偏振状态获得复杂新型光场，进而制备了各种新型的ZnO与ZnO/Ag纳米周期阵列结构，其精细纳米结构尺寸远小于激光波长以及衍射极限。分析表明，纳米花样的周期性排列是由光束干涉后的强度分布和偏振分布共同作用形成的。纳米结构阵列的获得为下一步有序复杂系统电子自旋的研究奠定了基础。
英文摘要	Electron spins in semiconductor nanostructures have prospective use in realization of solid-state qubits for quantum-information processing. There are a few important premises that need to be considered, such as long spin decoherence, short quantum-operation time and scalable qubits. Practical applications require that the above premises can be met at room temperature. In response to these requests, the paper focuses on the ultrafast dynamics and coherent manipulation of electron spins in II-VI colloidal quantum dots. What is more, due to that the colloidal quantum dots are usually simply-structured and in a state of disordered heap, we fabricate a variety of ordered periodic nanostructure arrays by using multiple interfered femtosecond laser pulses, which are expected to be used for spintronics research, especially to provide new ideas for scalable qubits. The main works and innovative results are as follows: (1) For the first time, we systematically study the spin decoherence dynamics of colloidal CdS quantum dots at room temperature, by using time-resolved Faraday rotation spectroscopy (TRFR). Long-lived spin coherence with is found at room temperature. From the magnetic field dependence of spin dephasing time, we conclude that hyperfine coupling mechanism dominates the electron spin dephasing in zero or low magnetic field. With increased magnetic fields, inhomogeneous dephasing becomes to take an important role. Moreover, in colloidal CdSe quantum dots, it has been found a similar spin-dephasing mechanism. (2) We investigate the ultrafast carrier and spin dynamics in CdTe single-core quantum dots and CdTe/CdS type II core-shell quantum dots at room temperature. The results show that: due to the electron-hole space separation in the type II core-shell quantum dots, it has longer carrier excitation and relaxation times than that in single-core quantum dots, and with the increase of shell thickness, the carrier excitation and relaxation times gradually increase. For the spin dynamics of CdTe or CdTe/CdS quantum dots, there is no significant spin precession signal, only a slowly monotonous decaying component has been observed in an external transverse magnetic field. (3) We investigate ultrafast rotation manipulation of spin coherent states in quantum dots at room temperature, using femtosecond laser pulses for the first time. As the wavelength of the control laser pulse is 800 nm used in spin coherent manipulation experiments, which has a large deviation from the resonance wavelength of the CdSe quantum dots (about 600 nm), we only obtained some elementary modulation signals. Nevertheless, it can still be seen that the optical stark effect based on femtosecond pulses could be used to realize the ultrafast coherent control of electron spins on a sub-picosecond timescale at room temperature. (4) We have fabricated complex periodic nanostructure arrays on ZnO and ZnO/Ag films, by using multi-beam interference of femtosecond laser pulses. A variety of new periodic nanostructure arrays have been produced by changing the laser intensity and polarization combinations. Among them, the sizes of fine structures are much smaller than the laser wavelength and its diffraction-limited scale. Theoretical calculation indicates that the periodic arrangements of these nano-patterns are attributed to the laser interferential intensity and polarization distributions together. The obtained nanostructure arrays could lay a solid foundation for the next research of electron spins in the complex orderly-structured systems.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15687]
专题	上海光学精密机械研究所_学位论文
推荐引用方式 GB/T 7714	李霞. 纳米半导体电子自旋超快光学调控中若干重要问题研究[D]. 中国科学院上海光学精密机械研究所. 2012.

个性服务

查看访问统计

相关权益政策

暂无数据

收藏/分享

除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。