立方体并非各向同性：CuInSnS$_4$单晶中的声子-激子解耦
When Cubic Is Not Isotropic: Phonon-Exciton Decoupling in CuInSnS$_4$ Single Crystals
AI总结：
研究揭示CuInSnS$_4$单晶中因In/Sn离子无序导致的局部对称破缺，影响声子和激子性质，通过多种光谱技术发现声子保持局域均匀而激子表现出强极化各向异性，为各向异性光电器件提供新机遇。
摘要：
原子尺度的无序可以在平均立方结构的晶体中产生隐藏的光学各向异性。本文显示CuInSnS$_4$单晶中存在由内在In/Sn离子无序引起的局部对称破缺环境，影响振动和激子性质的方式显著不同。结合偏振和温度依赖的拉曼光谱、红外近场显微镜、稳态和时间分辨光致发光以及第一性原理计算，发现声子在纳米尺度上基本保持对称平均和局域均匀。相比之下，光致发光显示低能带尾发射具有明显极化各向异性，遵循明确的角对称性，突显激子状态对局部对称破缺的强敏感性。这种声子-激子解耦表明，内在无序可以局域化激子同时保持振动相干和介电均匀性，从而在名义上立方的多价半导体中开辟新的极化敏感光源、各向异性光电探测器和基于激子的光学功能的新机遇。
英文摘要：
Atomic-scale disorder can create hidden optical anisotropy even in crystals that are structurally cubic on average. Here, we show that CuInSnS$_4$ single crystals host locally symmetry-broken environments arising from intrinsic In/Sn cation disorder, which affect vibrational and excitonic properties in markedly different ways. Combining polarization- and temperature-dependent Raman spectroscopy, infrared near-field microscopy, steady-state and time-resolved photoluminescence, and first-principles calculations, we find that phonons remain largely symmetry-averaged and locally homogeneous on the nanoscale. In contrast, photoluminescence reveals a lower-energy band-tail emission with pronounced polarization anisotropy following a well-defined angular symmetry, highlighting the strong sensitivity of excitonic states to local symmetry breaking. This phonon-exciton decoupling reveals that intrinsic disorder can localize excitons while preserving vibrational coherence and dielectric homogeneity, thereby opening new opportunities for polarization-sensitive light sources, anisotropic photodetectors, and exciton-based optical functionalities even in nominally cubic multinary semiconductors.
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