Department of Physics, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
Nano Lett. 2016 Sep 14;16(9):5568-73. doi: 10.1021/acs.nanolett.6b02118. Epub 2016 Aug 4.
It is well-known that excitonic effects can dominate the optical properties of two-dimensional materials. These effects, however, can be substantially modified by doping free carriers. We investigate these doping effects by solving the first-principles Bethe-Salpeter equation. Dynamical screening effects, included via the sum-rule preserving generalized plasmon-pole model, are found to be important in the doped system. Using monolayer MoS2 as an example, we find that upon moderate doping, the exciton binding energy can be tuned by a few hundred millielectronvolts, while the exciton peak position stays nearly constant due to a cancellation with the quasiparticle band gap renormalization. At higher doping densities, the exciton peak position increases linearly in energy and gradually merges into a Fermi-edge singularity. Our results are crucial for the quantitative interpretation of optical properties of two-dimensional materials and the further development of ab initio theories of studying charged excitations such as trions.
众所周知，激子效应对二维材料的光学性质具有主导作用。然而，通过掺杂自由载流子可以显著改变这些效应。我们通过求解第一性原理的 Bethe-Salpeter 方程来研究这些掺杂效应。通过保留总和规则的广义等离子体极点模型来考虑动态屏蔽效应，在掺杂体系中发现其非常重要。以单层 MoS2 为例，我们发现，在适度掺杂的情况下，激子结合能可以通过几百毫电子伏特来调节，而由于与准粒子能带隙重整化的抵消，激子峰位置几乎保持不变。在更高的掺杂密度下，激子峰位置在能量上呈线性增加，并逐渐合并成费米边缘奇点。我们的结果对于定量解释二维材料的光学性质以及进一步发展用于研究带电激子（如三电子）的从头算理论至关重要。
