The photoluminescence spectrum of a single-layer boron nitride remains elusive, marked by enigmatic satellites that hint at significant but unidentified exciton–phonon coupling. Here, by employing a first-principles approach based on the many-body cumulant expansion of the charge response, we calculate the optical absorption and photoluminescence of a single-layer boron nitride. We identify the specific exciton–phonon scattering channels and unravel their impact on the optical absorption and photoluminescence spectra, thereby providing an interpretation of the experimental features. Finally, we show that, even in a strongly polar material such as h-BN monolayer, the electron–hole interaction responsible for the excitonic effect results in the cancellation of the Frölich interaction at small phonon momenta. This effect is captured only if the invariance of the exciton–phonon matrix elements under unitary transformations in the Bloch function manifold is preserved in the calculation.

中文翻译：

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基于第一性原理累积量方法的单层氮化硼的光吸收和光致发光


单层氮化硼的光致发光光谱仍然难以捉摸，其标志是神秘的卫星，暗示着显着但未识别的激子-声子耦合。在这里，通过采用基于电荷响应的多体累积量展开的第一原理方法，我们计算了单层氮化硼的光学吸收和光致发光。我们识别了特定的激子-声子散射通道，并揭示了它们对光学吸收和光致发光光谱的影响，从而提供了对实验特征的解释。最后，我们表明，即使在 h-BN 单层等强极性材料中，引起激子效应的电子-空穴相互作用也会导致小声子动量下 Frölich 相互作用的抵消。只有在计算中保留布洛赫函数流形中酉变换下的激子-声子矩阵元素的不变性时，才能捕获这种效应。