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中国物理学会期刊

拓扑选择性非厄米趋肤效应

CSTR: 32037.14.aps.74.20250526

Topological selective non Hermitian skin effect

CSTR: 32037.14.aps.74.20250526
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  • 拓扑边界态因在带隙中的鲁棒性和无损耗的传输特性备受关注, 但在复杂系统中实现其稳定激发仍是一个挑战. 本文提出了一种利用亚对称性保护的边界态与长程非互易耦合系数, 实现具有拓扑选择性的非厄米趋肤效应 (non-Hermitian skin effect, NHSE) 的方法. 该方法能够选择性地对平庸体态施加非厄米趋肤效应, 同时保持拓扑边界态不受影响, 从而实现拓扑模式与体态模式在空间上的有效分离, 并在能带密集的系统中实现鲁棒的边界态激发. 此外, 本文将该模型扩展到二维体系, 实现了角态与体态模式的有效分离. 通过紧束缚模型进行理论预测, 分析了该模型中非厄米效应对能谱和趋肤性质的调控机制, 并利用有限元仿真在光学耦合环中验证了这一机制的可行性, 研究了非厄米趋肤效应的本征态特性, 并实现了拓扑态的鲁棒激发. 该机制将非厄米物理与拓扑光子学相结合, 为提升光子系统中信号的稳定性提供了新的思路与方向.

     

    Topologically protected waveguides have aroused increasing interest due to their robustness against disorder and defects. In parallel, the advent of non-Hermitian physics with its inherent gain-and-loss mechanisms has introduced new tools for manipulating wave localization and transport. However, most attempts to combine non-Hermitian effects with topological systems uniformly impose the non-Hermitian skin effect (NHSE) on all modes, without selectivity targeting topological states. In this work, we propose a scheme thatachieves topologically selective NHSE by combining sub-symmetry-protected boundary modes with long-range non-reciprocal couplings. In an improved Su–Schrieffer–Heeger (SSH) chain, we analytically demonstrate that robust zero-energy edge modes can be preserved even in spectra filled with bulk states, while selectively applying the NHSE to the trivial bulk states to achieve the spatial separation between topological state and bulk state. By adjusting the long-range couplings a non-Hermitian phase transition can be observed in the complex energy spectrum: it transitions from a closed loop (circle) to an open arc, and ultimately to a reversely coiled loop. These transitions correspond respectively to a leftward NHSE, the disappearance of the NHSE, and a rightward NHSE. According to the calculations of the generalized Brillouin zone (GBZ), we confirm this transition by observing the GBZ passing through the unit circle, indicating a change in the direction of NHSE.We further extend our model to a two-dimensional higher-order SSH lattice, where selective non-Hermitian modulation enables clear spatial separation between topological corner states and bulk modes. To quantify this, we compute the local density of states (LDOS) in the complex energy plane for site 0 (a topologically localized corner) and site 288 (a region exhibiting NHSE). The comparison of LDOS between the two sites reveals that the topological states are primarily localized at site 0, while the bulk states affected by NHSE accumulate at site 288.To validate the theoretical predictions, we perform finite-element simulations of optical resonator arrays by using whispering-gallery modes. By adjusting the coupling distances and incorporating gain/loss through refractive index engineering, we replicate the modified SSH model and confirm the selective localization of topological and bulk modes.Our results provide a robust method for selectively exciting and spatially controlling the topological states in non-Hermitian systems, and also lay a foundation for future low-crosstalk high-stability topological photonic devices.

     

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