Charged excitons in monolayer WSe2: Experiment and theory
Charged excitons in monolayer WSe2: Experiment and theory
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DOI：
10.1103/physrevb.96.085302
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发表时间：
2017-08-07
影响因子：
3.7
通讯作者：
Urbaszek, B.
中科院分区：
文献类型：
--
作者：
Courtade, E.;Semina, M.;Urbaszek, B.
单层过渡金属二硫属化物中的带电激子或 X-+/- Trion 具有数十 meV 的结合能。它们与中性激子 X-0 一起主导低温和高温下的发射光谱。我们使用基于封装在六方氮化硼中的 WSe2 单层的电荷可调器件来研究 X+ 和 X- 之间的结合能差异以及 X- 精细结构。我们发现在电荷中性状态下，X-0 发射在较低能量下伴随着接近纵向光学 (LO) 声子能量的强峰。该峰在反射率测量中不存在，其中仅 X-0 和 X-0 的激发态可见。在 n 掺杂体系中，我们发现发射率和反射率之间有更紧密的对应关系，因为观察到了 X- 具有良好解析的 6 meV 精细结构分裂的三重子跃迁。我们提出了不同 X+ 和 X- trion 态的对称性分析以及结合能计算的结果。我们将 n 和 p 掺杂方案的 Trion 结合能与低载流子浓度的模型计算进行比较。我们证明 X+ 和 X- trion 之间的分裂以及 X(-) 态的精细结构可能与电荷载流子之间的短程库仑交换相互作用有关。
Charged excitons, or X-+/- trions, in monolayer transition-metal dichalcogenides have binding energies of several tens of meV. Together with the neutral exciton X-0 they dominate the emission spectrum at low and elevated temperatures. We use charge-tunable devices based on WSe2 monolayers encapsulated in hexagonal boron nitride to investigate the difference in binding energy between X+ and X- and the X- fine structure. We find in the charge-neutral regime, the X-0 emission accompanied at lower energy by a strong peak close to the longitudinal optical (LO) phonon energy. This peak is absent in reflectivity measurements, where only the X-0 and an excited state of the X-0 are visible. In the n-doped regime, we find a closer correspondence between emission and reflectivity as the trion transition with a well-resolved fine-structure splitting of 6 meV for X- is observed. We present a symmetry analysis of the different X+ and X- trion states and results of the binding energy calculations. We compare the trion binding energy for the n- and p-doped regimes with our model calculations for low carrier concentrations. We demonstrate that the splitting between the X+ and X- trions as well as the fine structure of the X(-)state can be related to the short-range Coulomb-exchange interaction between the charge carriers.