Two-dimensional periodically driven systems can host an unconventional topological phase unattainable for equilibrium systems, termed the Anomalous Floquet-Anderson insulator (AFAI). The AFAI features a quasi-energy spectrum with chiral edge modes and a fully localized bulk, leading to non-adiabatic but quantized charge pumping. Here, we show how such a Floquet phase can be realized in a driven, disordered Quantum Anomalous Hall insulator, which is assumed to have two critical energies where the localization length diverges, carrying states with opposite Chern numbers. Driving the system at a frequency close to resonance between these two energies localizes the critical states and annihilates the Chern bands, giving rise to an AFAI phase. We exemplify this principle by studying a model for a driven, magnetically doped topological insulator film, where the annihilation of the Chern bands and the formation of the AFAI phase is demonstrated using the rotating wave approximation. This is complemented by a scaling analysis of the localization length for two copies of a quantum Hall network model with a tunable coupling between them. We find that by tuning the frequency of the driving close to resonance, the driving strength required to stabilize the AFAI phase can be made arbitrarily small.
Predicted photoinduced pair annihilation of emergent magnetic charges in the organic salt $α$-(BEDT-TTF)$_2$I$_3$ irradiated by linearly polarized light
长期的实验尝试，以找到磁单极子（即，在三维空间中具有孤立磁荷的基本粒子）尚未成功，尽管自1931年狄拉克提出以来进行了大量的努力。粒子物理学家已经预言了两个符号相反的磁荷可能发生碰撞和对湮灭。然而，如果这种湮灭存在，它的实验观测将是困难的，因为它的能量尺度被预测为非常高（$\sim$ 10 $^{16}$ GeV）。在目前的工作中，我们理论上预测使用Floquet理论，一对轻微的带隙的Dirac锥带在弱电荷有序的有机导体$α$ -（BEDT-TTF）$_2$ I $_3$，这表现为磁荷在动量空间中具有相反的符号，表现出对湮灭线偏振光照射下。这种光致对湮灭是伴随着一个非拓扑相变的Floquet正常绝缘体相的对比，众所周知的圆偏振光诱导的拓扑相变的Floquet陈省身绝缘体相。我们讨论了$α$ -（BEDT-TTF）$_2$ I $_3$具有能够实现合适的实验条件（即，非共振条件）和提供所需交错位置电势的电荷有序状态，从而提供了可用于观察预测的对湮灭现象的材料的罕见实例。并对实验观测的可行性进行了讨论。
