Quantum spin Hall effect spintronics

量子自旋霍尔效应自旋电子学

• 批准号: EP/T034343/1
• 负责人: Christopher Marrows
• 金额: $ 109.82万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FT034343%2F1
• 关键词: Quantum; spin; Hall; effect; spintronics

In this project we shall investigate the potential for spintronics of the quantum spin Hall (QSH) regime in hybrid nanostructures made by attaching ferromagnetic metal contacts to the edge states of two-dimensional topological insulators. These 2D materials will be formed from semiconducting InAs/GaSb coupled quantum wells. Being able to harness the spin-momentum-locked helical edge states in the QSH regime will have the potential for realising dramatic reductions in the power consumption of classical ICT hardware, and in the longer term offer the prospect of being useful for topological quantum computing. To build such spintronic devices, we need to know the conditions under which current flows through their edge states. We need to know the spin polarisation of a current injected from a ferromagnet into the QSH edge state, and which ferromagnetic contact material provides the largest spin-polarisation. We need to know how efficiently spins can be injected and detected in these QSH edge channels using ferromagnetic metal contacts. We also need to know over what distance spin information can propagate in the QSH edge states, and in what circumstances this distance is the longest.The project is a collaboration between the School of Physics and Astronomy, who have expertise in spintronics and the study of devices incorporating ferromagnetic materials, as well as topological materials, and the School of Electronic and Electrical Engineering, who are capable of growing ultra-high quality InAs/GaSb coupled quantum wells in their III-V semiconductor molecular beam epitaxy system. We will begin by constructing contacted InAs/GaSb mesas with top and bottom gates that allow them to be tuned into a charge-neutral and non-trivial regime, which are the correct conditions for current to flow only in the edge states. We will attach normal drain contacts on either side of a ferromagnetic source contact on a InAs/GaSb mesa and measure the drain currents from left- and right-flowing edge states in the non-trivial edge state regime; the spin-momentum locking in the QSH edge states will mean that these spatially separated currents directly correspond to the spin-resolved currents, allowing a direct measurement of the spin-polarisation of the current injected from the ferromagnet. We shall try different ferromagnetic metals to determine which one works best. We will then study the flow of a current in a QSH edge state between two closely-spaced ferromagnetic contacts, which is expected to be larger when the current flow direction is spin-momentum locked to the majority spin direction of the contacts; reversing the magnetisation direction in the contacts will invert this diode-like behaviour. The difference between forward and reverse currents will tell us the efficiency of the spin injection and detection. Moving the contacts apart will allow us to determine the length over which spins can flow coherently within the edge states by measuring the decline in difference between forward and reverse currents with spacing; we shall study this as a function of temperature in order to determine the physical mechanisms causing the loss of spin coherence. The results we shall obtain will not only lead to high impact publications and conference presentations by shedding light on the possibilities offered by this novel combination of materials, but also develop valuable know-how in the field of quantum spin Hall spintronics for technological applications.

在这个项目中，我们将研究量子自旋霍尔（QSH）体系在混合纳米结构中的自旋电子学的潜力，这种结构是通过将铁磁性金属触点附着在二维拓扑绝缘体的边缘状态上而制成的。这些二维材料将由半导体InAs/GaSb耦合量子阱形成。能够利用QSH体制中的自旋动量锁定螺旋边缘状态，将有可能实现经典ICT硬件功耗的大幅降低，并且从长远来看，为拓扑量子计算提供了有用的前景。为了制造这样的自旋电子器件，我们需要知道电流流过它们边缘状态的条件。我们需要知道从铁磁体注入到QSH边缘状态的电流的自旋极化，以及哪种铁磁接触材料提供最大的自旋极化。我们需要知道使用铁磁金属触点在这些QSH边缘通道中如何有效地注入和检测自旋。我们还需要知道自旋信息在QSH边缘状态中传播的距离，以及在什么情况下这个距离最长。该项目是物理与天文学院和电子与电气工程学院之间的合作，前者在自旋电子学和结合铁磁材料和拓扑材料的器件研究方面具有专长，后者能够在其III-V半导体分子束外延系统中生长超高质量的InAs/GaSb耦合量子阱。我们将首先构建带有顶部和底部栅极的接触式InAs/GaSb台面，使它们能够调谐到电荷中性和非琐碎的状态，这是电流仅在边缘状态下流动的正确条件。我们将在InAs/GaSb平台上的铁磁源触点两侧连接正常漏极触点，并在非平凡边缘状态下测量左流和右流边缘状态下的漏极电流；QSH边缘状态的自旋动量锁定将意味着这些空间分离的电流直接对应于自旋分辨电流，从而可以直接测量从铁磁体注入的电流的自旋极化。我们将尝试不同的铁磁性金属，以确定哪一种效果最好。然后，我们将研究两个紧密间隔的铁磁触点之间在QSH边缘状态下的电流流动，当电流流向自旋动量锁定在触点的大部分自旋方向时，预计电流会更大；改变触点的磁化方向将扭转这种类似二极管的行为。正向电流和反向电流之间的差异将告诉我们自旋注入和检测的效率。将触点分开将使我们能够通过测量正向和反向电流之间的差值随间距的减小来确定自旋在边缘状态内能够连贯流动的长度；我们将把它作为温度的函数来研究，以便确定导致自旋相干性丧失的物理机制。我们将获得的结果不仅会通过揭示这种新型材料组合所提供的可能性而导致高影响力的出版物和会议报告，而且还会在量子自旋霍尔自旋电子学领域为技术应用开发有价值的专有技术。