Efficient manipulation of magnons for information processing is a central topic in spintronics and magnonics. An outstanding challenge for long-distance spin transport with minimal dissipation is to overcome the relaxation of magnons and to amplify the spin current they carry. Here, we propose to amplify magnon currents based on the realization of the bosonic Klein paradox in magnetic nanostructures. This paradox involves the magnon's antiparticle, the antimagnon, of which the existence is usually precluded by magnetic instabilities as it is an excitation at negative energy. We show that, by appropriately tuning the effective dissipation through spin-orbit torques, both magnons and antimagnons are dynamically stabilized. As a result, we find that the reflection coefficient of incident magnons at an interface between two coupled magnets can become larger than one, thereby amplifying the reflected magnon current. Our findings can lead to magnon amplifier devices for spintronic applications. Furthermore, our findings yield a solid-state platform to study the relativistic behavior of bosonic particles, which is an outstanding challenge with fundamental particles.
Anomalous Klein paradox due to misalignment of optically-tunable elliptical dispersion for Dirac-cone dressed states and direction of incoming particles
Quantization Mapping on Dirac Dynamics via Voltage-Driven Charge Density in Monolayer Graphene: A Klein Paradox and Entropy-Ruled Wavevector Mechanics Study
KPR Institute of Engineering and Technology（KPR工程技术学院）
Dynamical Stabilization of Inverted Magnetization and Antimagnons by Spin Injection in an Extended Magnetic System
ETH Zurich（苏黎世联邦理工学院）；Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg（斯特拉斯堡大学，法国国家科学研究中心，斯特拉斯堡材料物理与化学研究所）；Université Grenoble Alpes, CNRS, Institut Néel（格勒诺布尔阿尔卑斯大学，法国国家科学研究中心，尼尔研究所）；University of Konstanz（康斯坦茨大学）
Chiral Bloch states in single layer graphene with Rashba spin-orbit coupling: Spectrum and spin current density
研究了单层石墨烯中二维无质量Dirac电子在一维周期Kronig-Penney势和Rashba自旋轨道耦合作用下的Bloch谱和自旋物理。克莱因悖论揭示了能带色散和石墨烯自旋电子学的新特征。（1）Bloch能量色散$\veps(p)$具有特殊的结构：在Bloch动量$\pm p \ne 0$处有{ \it两个Dirac点}，在宽的价带和导带之间出现一个窄带。(2)电荷流和自旋密度矢量消失。(3)然而，所有的自旋流密度张量的非对角元素是有限的，它们的大小与自旋轨道强度线性增加。特别地，存在极化垂直于石墨烯平面的自旋密度电流。(4)自旋密度流是空间相关的，因此它们的连续性方程包括有限的自旋力矩密度。
