Spintronics of helical edge states interacting with a quantum magnet

螺旋边态的存在是二维拓扑绝缘体的一个重要特征。这些边缘态在没有时间反演对称性破缺场的情况下对单粒子背散射是免疫的。在螺旋边缘态附近放置磁性绝缘体，交换场将在螺旋边缘态谱中打开一个间隙。令人惊讶的是，当磁体具有适当对齐的易平面各向异性的自身动力学时，施加偏压将磁体设置在旋进模式中，其中磁体以这样的方式泵送电荷，即恢复量子自旋霍尔电导，尽管在螺旋边缘的激发光谱中存在间隙。这导致了有趣的输运和噪声特性，并被提议成为实现绝热量子马达的平台。在我们之前的联合工作[Silvestrov，Recher和Brouwer，Phys. Rev. B 93，205130（2016）]的基础上，我们在这里提出将这个显着系统的研究扩展到新的方向，例如热电效应，并考虑我们和其他人在以前的出版物中使用的理想化模型描述之外的方面。具体而言，在第一组子项目中，我们解决了热电应用的易平面磁绝缘体交换耦合到螺旋边缘，和设备的应用，如“热磁化”，“热量子电机”，和介观“电子冷却器”。这里的其他研究方向包括非线性输运，低频噪声和磁化波动以及量子干涉效应。建议的后半部分将致力于理想化模型的推广。我们计划使用的朗道-Lifshitz方程的描述的电流/偏置驱动的动态设置与较少的对称性比原来的出版物。在电流-电压特性和磁化动力学的新的有趣的功能。其他提出的问题包括具有多个自由度的磁体和金属磁体的情况。

The existence of helical edge states is a key feature of a two-dimensional topological insulator. These edge states are immune against single-particle backscattering in the absence oftime-reversal symmetry breaking felds. Placing a magnetic insulator in proximity to the helical edge states, the Exchange field will open a gap in the helical edge state spectrum.Surprisingly, when the magnet has its own dynamics with a properly aligned easy-plane anisotropy, the application of a voltage bias sets the magnet in a precessional mode in which the magnet pumps charge in such a way that the quantized quantum spin Hallconductance is restored, in spite of the presence of a gap in the excitation spectrum of the helical edge. This leads to intriguing transport and noise properties, and was proposed to bea platform for the realization of an adiabatic quantum motor.Building on our previous joint work [Silvestrov, Recher, and Brouwer, Phys. Rev. B 93, 205130 (2016)], we here propose to extend the study of this remarkable system into new directions,such as thermoelectric effects, and consider aspects beyond the idealized model description used in previous publications by us and others. Specifically, in a first set of subprojects we address thermoelectric applications of an easy-plane magnetic insulator exchange-coupled to a helical edge, and device applications such as "thermomagnetization", a "thermal quantum Motor", and a mesoscopic "electron cooler". Other directions of research here include nonlinear transport, low frequency noise and magnetization fluctuations as well as quantum interference effects. The second half of the proposal will be devoted to generalizations of theidealized model. We plan to use the Landau-Lifshitz equation for the description of the current/bias driven dynamics of a Setup with less symmetries than in the original publications. New interesting features in current-voltage characteristics and magnetization dynamics are expected. Other proposed Problems include the case of a magnet with several degrees of freedom and a metallic magnet.