[论文解读] Anomalous transport regime in non-Hermitian, Anderson-localizing hybrid systems

Himadri Nath Sahoo, R Vijay+1 more|arXiv (Cornell University)|Jun 10, 2022

Quantum and electron transport phenomena被引用 6

一句话总结

本研究通过实验展示了在一维非厄米混合系统中，由伪表面等离子体极化激元（SSPPs）与光子组成的强无序体系中存在一种异常输运行为。尽管安德森局域化在传统体系中会抑制输运，但作者观察到由于形成非正交、共存的局域模态而产生的类项链态，进而形成能带，导致传输增强，该现象通过广义电导率 ⟨g′⟩ > 1 及金属态下的高斯分布电导值得到证实。

ABSTRACT

In a disordered environment, the probability of transmission of a wave reduces with increasing disorder, the ultimate limit of which is the near-zero transmission due to Anderson localization. Under localizing conditions, transport is arrested because the wave is trapped in the bulk of the sample with decaying-exponential coupling to the boundaries. Any further increase in disorder does not modify the overall transport properties. Here, we report the experimental demonstration of a hitherto-unrealized anomalous transport of hybrid particles under localizing disorder in a non-Hermitian setting. We create hybrid polariton-photon states in a one-dimensional copper sample with a comb-shaped periodic microstructure designed for microwave frequencies. Metallic dissipation realizes the necessary non-Hermiticity. Disorder is introduced by deliberate alterations of the periodic microstructure. Direct measurement of wave-functions and phases was achieved by a near-field probe. At a particular disorder, We observe the onset of Anderson localization of the hybrid states endorsed by exponential tails of the wavefunction. However, at stronger disorder and under conditions that support localization, an unexpected enhancement in the transmission was facilitated by an emergent mini-band. The transmission was traced to the hopping of the hybrid particle over multiple co-existing localized resonances that exchange energy due to the non-orthogonality. These emergent states are manifested in all configurations under strong disorder, suggesting the formation of a novel transport regime. This is verified by measuring the averaged conductance which endorses an anomalous transport regime in the hybrid, non-Hermitian environment under strong disorder. These experimental observations open up new unexplored avenues in the ambit of disorder under non-Hermitian conditions.

研究动机与目标

• 研究在强无序条件下混合非厄米体系中的输运行为，此时传统局域化会抑制传输。
• 探讨非厄米性与模态杂化是否能在局域化无序条件下稳定导电态。
• 通过直接测量波函数与相位，实验验证超越标准局域化的新输运行为的存在。
• 表征电导的统计分布，并在强无序非厄米环境中识别金属行为的特征。

提出的方法

• 制备了一维铜样品，其具有梳状周期性微结构，可在微波频率下支持伪表面等离子体极化激元（SSPPs）。
• 通过有意识地改变周期性微结构引入可控无序，以调节局域化强度。
• 采用近场探针直接测量杂化波函数的空间分布与相位。
• 在多个无序构型下测量广义电导率 ⟨g′⟩，以评估输运特性。
• 分析电导分布 P(g′)，并与一维无序体系在局域化转变附近的理论模型进行比较。
• 利用数值模拟验证观测到的波函数相位跃迁及类项链态的组分结构。

实验结果

研究问题

• RQ1 非厄米混合体系是否能在通常引发安德森局域化的条件下表现出增强输运？
• RQ2 在强无序下导致异常传输的涌现态的本质是什么？
• RQ3 该体系中电导的统计特性与传统局域态或金属态下的表现有何异同？
• RQ4 局域模态的非正交性在无序体系中多在多大程度上促进能量交换与能带形成？
• RQ5 在强无序下，异常输运行为是否在所有构型中均保持稳定，其量化方式如何？

主要发现

• 在中等无序下，观察到传统安德森局域化，表现为波函数尾部呈指数衰减，电导 ⟨g′⟩ < 1，符合绝缘行为。
• 在强无序下，广义电导率 ⟨g′⟩ 急剧上升至 1.2（高斯拟合得 ⟨g′⟩ = 1.16），表明尽管存在绝缘性无序，仍呈现类金属行为。
• 异常输运区的电导分布 P(g′) 呈高斯分布，与局域区的对数正态分布形成鲜明对比，证实了扩展的、类金属态的存在。
• 类项链态——多个局域共振态的相干叠加——在所有高无序构型中持续存在，并通过近场探测直接成像。
• 波函数中的相位跃迁证实了类项链态内部存在多个共存的局域模态，与数值模拟结果高度一致。
• 异常输运行为局域在杂化频率（4.5 GHz）附近，由于频率钉扎与受限迁移，导致涌现能带的形成。