发表机构
Technical University of Kenya（肯尼亚科技大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过精确对角化Holstein-激子模型，发现质量不对称破坏交换选择规则，使激子获得极化子云，而解离边界由全局能量平衡决定，揭示了对称性对激子dressing与稳定化的矛盾作用。
AI 中文摘要
在极性材料中，中性激子通过电子和空穴形变势之和与声子耦合。由于总源项因电荷中性而消失，弹性激子-声子顶点通过电子-空穴干涉被正则化。这里，我们通过对 Holstein-激子模型的精确对角化来确定这种干涉的非微扰命运。通过参数化质量不对称以将其与小极化子原子极限解耦，我们绘制了一个包含内部 dressing 交叉和解离边界的相图。我们解析地证明并数值验证了，对于等质量情况，对称激子基态受到精确交换选择规则的保护而免受声子 dressing，前提是声子源在电子-空穴交换下为奇函数（中性情况）。随着质量不对称的增加，该选择规则被破坏，激子获得强的局域极化子云。我们表明，解离边界相反地由库仑束缚与极化子稳定化之间的全局能量平衡决定，并且几乎独立于内部 dressing。矛盾的是，保护激子免受 dressing 的对称性却剥夺了其极化子稳定化，在强耦合下促使其走向解离。我们在晶格激子-极化子模型的背景下讨论这些结果，及其对质量对称与质量不对称极性半导体中尖锐与宽激子线的意义。
英文摘要
In a polar material, a neutral exciton couples to phonons through the sum of the electron and hole deformation potentials. Because the total source vanishes by charge neutrality, the elastic exciton-phonon vertex is regularized by electron-hole interference. Here we determine the non-perturbative fate of this interference by exact diagonalization of a Holstein-exciton model. By parameterizing the mass asymmetry to decouple it from the small-polaron atomic limit, we map a regime map comprising an internal dressing crossover and a dissociation boundary. We prove analytically and verify numerically that for equal masses, the symmetric exciton ground state is protected from phonon dressing by an exact exchange selection rule, provided the phonon source is odd under electron-hole exchange (the neutral case). As mass asymmetry increases, this selection rule is broken and the exciton acquires a strong local polaronic cloud. We show that the dissociation boundary, conversely, is set by a global energy balance between Coulomb binding and polaronic stabilization, and is nearly independent of the internal dressing. Paradoxically, the very symmetry that protects the exciton from dressing denies it polaronic stabilization, driving it toward dissociation at strong coupling. We discuss these results in the context of lattice exciton-polaron models and their implications for sharp versus broad excitonic lines in mass-symmetric versus mass-asymmetric polar semiconductors.
Comments7 papges, 5 figures
