Cudazzo Pierluigi, Sponza Lorenzo, Giorgetti Christine, Reining Lucia, Sottile Francesco, Gatti Matteo
Laboratoire des Solides Irradiés, École Polytechnique, CNRS, CEA, Université Paris-Saclay, F-91128 Palaiseau, France.
European Theoretical Spectroscopy Facility (ETSF).
Phys Rev Lett. 2016 Feb 12;116(6):066803. doi: 10.1103/PhysRevLett.116.066803. Epub 2016 Feb 10.
Low-dimensional materials differ from their bulk counterparts in many respects. In particular, the screening of the Coulomb interaction is strongly reduced, which can have important consequences such as the significant increase of exciton binding energies. In bulk materials the binding energy is used as an indicator in optical spectra to distinguish different kinds of excitons, but this is not possible in low-dimensional materials, where the binding energy is large and comparable in size for excitons of very different localization. Here we demonstrate that the exciton band structure, which can be accessed experimentally, instead provides a powerful way to identify the exciton character. By comparing the ab initio solution of the many-body Bethe-Salpeter equation for graphane and single-layer hexagonal boron nitride, we draw a general picture of the exciton dispersion in two-dimensional materials, highlighting the different role played by the exchange electron-hole interaction and by the electronic band structure. Our interpretation is substantiated by a prediction for phosphorene.
低维材料在许多方面与其体相材料不同。特别是，库仑相互作用的屏蔽作用被大大削弱，这可能会产生重要影响，例如激子结合能显著增加。在体相材料中，结合能被用作光谱中的一个指标来区分不同类型的激子，但在低维材料中这是不可能的，因为在低维材料中，结合能很大，对于定位非常不同的激子来说，其大小相当。在这里，我们证明了可以通过实验获得的激子能带结构，反而提供了一种识别激子特性的有力方法。通过比较针对石墨烷和单层六方氮化硼的多体贝特 - 萨尔皮特方程的从头算解，我们描绘了二维材料中激子色散的总体情况，突出了交换电子 - 空穴相互作用和电子能带结构所起的不同作用。我们的解释通过对磷烯的预测得到了证实。
