In cavity quantum electrodynamics, the multiple reflections of a photon between two mirrors defining a cavity is exploited to enhance the light-coupling of an intra-cavity atom. We show that this paradigm for enhancing the interaction of a flying particle with a localized object can be generalized to spintronics based on van der Waals 2D magnets. Upon tunneling through a magnetic bilayer, we find the spin transfer torques per electron incidence can become orders of magnitude larger than $\hbar/2$, made possible by electron's multi-reflection path through the ferromagnetic monolayers as an intermediate of their angular momentum transfer. Over a broad energy range around the tunneling resonances, the damping-like spin transfer torque per electron tunneling features a universal value of $\frac{\hbar}{2} \tan{\frac{\theta}{2}}$, depending only on the angle $\theta$ between the magnetizations. These findings expand the scope of magnetization manipulations for high-performance and high-density storage based on van der Waals magnets.

中文翻译：

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原子级薄磁性双层中的巨大自旋转移扭矩

在腔量子电动力学中，利用定义腔的两个镜子之间光子的多次反射来增强腔内原子的光耦合。我们表明，这种增强飞行粒子与局部物体相互作用的范例可以推广到基于范德瓦尔斯 2D 磁体的自旋电子学。在穿过磁性双层时，我们发现每个电子入射的自旋转移扭矩可以变得比 $\hbar/2$ 大几个数量级，这是通过电子通过铁磁单层的多次反射路径作为其角动量转移的中间体而实现的. 在隧穿共振周围的宽能量范围内，每个电子隧穿的类似阻尼的自旋转移扭矩具有通用值 $\frac{\hbar}{2} \tan{\frac{\theta}{2}}$，仅取决于磁化之间的角度 $\theta$。这些发现扩展了基于范德华磁铁的高性能和高密度存储的磁化操作范围。