Exceptional points in dissipatively coupled spin dynamics
Exceptional points in dissipatively coupled spin dynamics
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DOI：
10.1103/physrevresearch.2.013031
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发表时间：
2019-11
影响因子：
4.2
通讯作者：
Y. Tserkovnyak
中科院分区：
文献类型：
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作者：
Y. Tserkovnyak
我们从理论上研究了通过各向同性介质交换耦合的经典自旋的动力学。耦合在介质响应的绝热水平上进行处理，它介导一阶频率耗散相互作用以及瞬时海森堡交换。由此产生的阻尼自旋进动在耦合自旋动力学中产生异常点（EP），这应该可以通过现有的磁性异质结构通过实验获得。特别是，我们表明，通过控制局部阻尼，可以在反铁磁二聚体中自然地接近 EP，而通过调整铁磁情况下自旋之间的耗散耦合来实现同样的效果。将我们的处理扩展到一维自旋链，我们展示了如何通过调整耗散特性在布里渊幅角区内出现 EP。 EP 对从布里渊区中心出现的临界点，在磁振子谱中实现无间隙外尔点。在铁磁和反铁磁情况下，将阻尼调节到超过此临界点会在有限的动量范围内产生磁振子模式的同步（水平吸引）。因此，我们确定阻尼磁振子通常可以在其能带结构中产生奇点，接近奇点时，它们的运动学特性（例如群速度）对控制参数变得极其敏感。
We theoretically investigate dynamics of classical spins exchange-coupled through an isotropic medium. The coupling is treated at the adiabatic level of the medium's response, which mediates a first-order in frequency dissipative interaction along with an instantaneous Heisenberg exchange. The resultant damped spin precession yields exceptional points (EPs) in the coupled spin dynamics, which should be experimentally accessible with the existing magnetic heterostructures. In particular, we show that an EP is naturally approached in an antiferromagnetic dimer by controlling local damping, while the same is achieved by tuning the dissipative coupling between spins in the ferromagnetic case. Extending our treatment to one-dimensional spin chains, we show how EPs can emerge within the magnonic Brillouin zone by tuning the dissipative properties. The critical point, at which an EP pair emerges out of the Brillouin zone center, realizes a gapless Weyl point in the magnon spectrum. Tuning damping beyond this critical point produces synchronization (level attraction) of magnon modes over a finite range of momenta, both in ferro- and antiferromagnetic cases. We thus establish that damped magnons can generically yield singular points in their band structure, close to which their kinematic properties, such as group velocity, become extremely sensitive to the control parameters.