Giant Spin Transfer Torque in Atomically Thin Magnetic Bilayers

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 thanℏ/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(ℏ/2)tan(θ/2),depending only on the angleθbetween the magnetizations.These findings expand the scope of magnetization manipulations for high-performance and high-density storage based on van der Waals magnets.

Distinct moiré textures of in-plane electric polarizations for distinguishing moiré origins in homobilayers

In binary compound 2D insulators/semiconductors such as hexagonal boron nitride(h BN), the different electron affinities of atoms can give rise to out-of-plane electric polarizations across inversion asymmetric van der Waals interface of near 0° interlayer twisting. Here we show that at a general stacking order where sliding breaks 2π/3-rotational symmetry, the interfacial charge redistribution also leads to an in-plane electric polarization, with a magnitude comparable to that of the out-of-plane ones.The effect is demonstrated in h BN bilayers, as well as in biased graphene bilayers with gate-controlled interlayer charge redistributions. In long wavelength moiré patterns, the in-plane electric polarizations determined by the local interlayer stacking registries constitute topologically nontrivial spatial textures. We show that these textures can be used to distinguish moirépatterns of different origins from twisting, biaxial-and uniaxial-heterostrain, where vector fields of electric polarizations feature Bloch-type merons, Néel-type merons, and anti-merons, respectively. Combinations of twisting and heterostrain can further be exploited for engineering various electric polarization textures including 1D quasiperiodic lattices.

摩尔超晶格中电场可调的极化激元拓扑输运

在由不同的单层过渡金属硫族化合物堆叠形成的双层范德瓦尔斯异质结中,两层之间的微小转角可导致摩尔超晶格的出现,其基态光学性质由位于不同层的电子和空穴通过库仑吸引形成的层间激子主导.层间激子携带的静电偶极矩使得它可以通过静电势来操控其定向流动,同时层间激子也具有一定的光学跃迁偶极矩,它的大小和方向随层间激子在摩尔超晶格中的位置而变化.本文指出摩尔超晶格中的层间激子与二维平面光学微腔内光子模的杂化可产生两种具备不同拓扑性质的摩尔极化激元,可导致自旋/谷霍尔效应和偏振霍尔效应.通过调节两层间的电压改变层间激子与光学腔内光子模的失谐量,可选择特定种类的摩尔极化激元,这使得它的拓扑输运现象具备卓越的电场可调性.