金属邻近效应对激子的异常稳定作用
Anomalous stabilization of excitons by metallic proximity
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中文总结 AI 辅助
本文研究PdxCu1-xCrO2薄膜跨逾渗驱动金属-绝缘体相变的激子态，发现孤立金属区域可增强激子结合能，揭示金属-激子异常共存，提出纳米级金属邻近效应可修饰激子相互作用。
中文摘要 AI 辅助
金属环境通常被认为会通过强介电屏蔽作用抑制激子，但在金属与绝缘区域共存的复合体系中，其影响可能有所不同。本文研究了PdxCu1-xCrO2薄膜中跨逾渗驱动金属-绝缘体相变的激子态。光学光谱和多体GW计算表明，CuCrO2拥有结合能约为489 meV的强束缚激子。随着Pd替代量增加，体系在x=0.5附近趋近于绝缘体-金属相变，与三角晶格的位点逾渗阈值一致。在逾渗前区域，激子共振红移241 meV，而Tanguy连续谱起始点几乎保持不变，这与金属化前激子结合能显著增加的情况一致。基于镜像电荷的激子氢模型显示，孤立金属区域可通过镜像电荷相互作用增强电子-空穴束缚，而一旦形成连续金属网络，常规屏蔽效应便会恢复。尽管该模型为观测到的激子演化提供了一种可能的解释，但不能排除另一种场景，即金属响应与激子响应源自电子上截然不同的状态且独立演化。这些结果揭示了逾渗驱动金属-绝缘体相变附近存在不寻常的金属-激子共存，并表明纳米级金属邻近效应是修饰激子相互作用的可行途径。
英文摘要
Metallic environments are generally expected to suppress excitons through strong dielectric screening, yet their influence can differ in composite systems where metallic and insulating regions coexist. Here, we investigate excitonic states in PdxCu1-xCrO2 thin films across a percolation-driven metal-insulator transition. Optical spectroscopy and many-body GW calculations show that CuCrO2 hosts strongly bound excitons with a binding energy of about 489 meV. With increasing Pd substitution, the system approaches an insulator-to-metal transition near x = 0.5, consistent with the site-percolation threshold of a triangular lattice. In the pre-percolation regime, the excitonic resonance redshifts by 241 meV while the Tanguy continuum onset remains nearly unchanged, consistent with a substantial increase in exciton binding energy before metallization. An image-charge-based excitonic hydrogen model shows that isolated metallic regions can enhance electron-hole binding through image-charge interactions, whereas conventional screening is recovered once a continuous metallic network forms. Although this model provides a possible interpretation of the observed excitonic evolution, an alternative scenario in which metallic and excitonic responses originate from electronically distinct states and evolve independently cannot be excluded. These results reveal unusual metallic-excitonic coexistence near a percolation-driven metal-insulator transition and suggest nanoscale metallic proximity as a possible route for modifying excitonic interactions.
