%A Weihao Cao, Matisse Wei-Yuan Tu, Jiang Xiao, and Wang Yao %T Giant Spin Transfer Torque in Atomically Thin Magnetic Bilayers %0 Journal Article %D 2020 %J Chin. Phys. Lett. %R 10.1088/0256-307X/37/10/107201 %P 107201%V 37 %N 10 %U {https://cpl.iphy.ac.cn/CN/abstract/article_105742.shtml} %8 2020-09-12 %X 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 that 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 $(\hbar/2)\tan (\theta /2)$, 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.