低维耦合量子体系中混合空穴基态及自旋调控研究

Because of potential applications in novel optoelectronic devices or quantum information processing, the low dimensional coupled quantum systems have been the focus of much research.In this project, we aim at studying physical properties of the hole ground state and manipulation of hole spin under electric and magnetic fields in low dimensional coupled quantum systems. The main work include the following four points: .(1)In coupled system, the electronic states, being bounding-like ground states, is mostly based on single-band effective-mass approximations, but the valence hole shows more complex feature. Since the two uppermost P-like valence band is subject to a strong spin-orbit (SO) interaction, which leads to a sizeable coupling of heavy-hole (HH) and light-hole (LH) subbands. Our studies showed that the ground states of a valence hole in coupled quantum dots show an anti-bounding-like character. By means of multi-band KoP approximation, We will investigate the properties of hole orbital taking into account the effects of LH-HH mixture, spin-orbit interaction, strain and exchange correlation. By revealing the coupling hole state orbit and anti-cross characteristics, The results can access to the key physical parameters of coupled quantum hole ground state in low-dimensional system ..(2)We will study correlation between the properties of hole state and quantum effects such as confinement, quantum tunneling and spin-orbital coupling under external electric and magnetic field. In addition, tuning of hole g factors under external fields is also explored. This work provides a flexible mechanism to maniplantion the ground state spin through manipulation of the electirc and magnetic field..(3)For one-dimensional coupled quantum wires, we will explore the similarities and differences of hole state characteristics between one-dimensional confinement and zero-dimensional system..(4)We condisder what happens when we add additional holes to the coupled system. With the multi-hole state,impact of hole numbers on the behavior of bonding or antibonding ground state will be analyzed. .All these studies not only benefit the deep understanding of hole spin theories in low dimensional coupled semiconductors. but also provide theoretical basis and direction for future spin quantum manipulation.

在量子计算、量子信息和光电子技术等方面的潜在应用，低维半导体量子结构的耦合调控逐渐受到广泛关注。本项目拟开展低维耦合量子体系中混合空穴基态的物理特性及电磁场下空穴自旋-轨道相互作用机理的研究，通过建立外电磁场下体系的轻重空穴耦合、自旋轨道作用、应变场和交换关联等模型，探讨不同空穴电荷分布对系统基态成键和反键特征的影响，揭示耦合空穴态的轨道特征和反交叉行为；基于波函数的分布，弄清轨道-自旋相互作用与耦合体系的对称性及距离的关系，实现磁场对空穴基态自旋分布的控制；进一步针对零维/一维耦合量子结构，通过调节量子结构间的量子隧穿和空穴态的关联，弄清限域体系自旋-轨道相互作用的空穴g因子与外场的关系，获得共振耦合条件下半导体耦合量子结构的空穴基态性质的演变及自旋分布。研究结果有助于深层次理解和认识低维耦合体系中空穴轨道和自旋分布的反常特征，为未来基于耦合体系的自旋量子调控应用提供相应的理论基础。

低维半导体量子结构的耦合调控在固态量子计算和量子信息方面受到了广泛关注。本项目使用多带K•P理论和紧束缚原子方法，建立外电磁场下体系的轻重空穴耦合、自旋轨道作用、应变场和交换关联等模型，开展了耦合体系内低维耦合量子体系中混合空穴基态的物理特性的研究，探讨了内在极化和电磁场调控下耦合体系中空穴自旋-轨道相互作用机理，揭示了多带耦合的情况下, 耦合体系中价带基态能级和激发态能级之间反交叉现象；研究发现随着耦合距离的增加, 量子点基态轻重空穴波函数的比重发生变化,导致量子点空穴基态波函数从成键态反转成为反成键态。 同时因空穴基态及激发态波函数特性的转变, 电子、空穴的基态及激发态波函数的叠加强度发生的明显变化，系统地分析了耦合量子体系在不同耦合强度下价带空穴的变化规律,提出了采用计算价带基态和激发态波函数与导带基态波函数交叠趋势来判断量子点价带基态波函数属性的方法。探讨了内部极化和应变效应下，轻重空穴及轨道相互作用对耦合量子点空穴基态反成键态特性的影响，结果表明，应变效应改变了顶部（底部）量子点内空穴的束缚势能，使得空穴基态波函数较多局域在底部量子点中。同时随着耦合强度的变化,价带基态能级和激发态能级发生反交叉现象，基态从成键态翻转为反成键态。同时，应变效应使得量子点的重空穴及轻空穴的能带发生改变，轻重空穴耦合减弱，基态和激发态之间发生成键、反成键态翻转的临界距离明显减小。研究了量子点体系的自旋纯度，实现磁场对量子点空穴基态之间的耦合的调制作用。探讨了量子点内的各向异性，此各向异性来源于量子点有效质量、形态尺寸、外场调控及内部极化等。体系内各向异性的存在导致了三维空间量子束缚的变化，体系中出现了轻空穴基态，并且此各向异性可实现对体系中空穴带的自旋调制及带间耦合。研究结果有助于深层次理解和认识低维耦合体系中空穴轨道和自旋分布的反常特征，为未来基于耦合体系的自旋量子调控应用提供相应的理论基础。