Department of Physics and Center for Complex Quantum Systems, University of Texas at Austin, Austin, Texas 78712, USA.
Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Technische Universität Berlin, 10623 Berlin, Germany.
Nat Commun. 2017 Jun 28;8:15552. doi: 10.1038/ncomms15552.
In atomically thin transition metal dichalcogenides (TMDs), reduced dielectric screening of the Coulomb interaction leads to strongly correlated many-body states, including excitons and trions, that dominate the optical properties. Higher-order states, such as bound biexcitons, are possible but are difficult to identify unambiguously using linear optical spectroscopy methods. Here, we implement polarization-resolved two-dimensional coherent spectroscopy (2DCS) to unravel the complex optical response of monolayer MoSe and identify multiple higher-order correlated states. Decisive signatures of neutral and charged inter-valley biexcitons appear in cross-polarized two-dimensional spectra as distinct resonances with respective ∼20 and ∼5 meV binding energies-similar to recent calculations using variational and Monte Carlo methods. A theoretical model considering the valley-dependent optical selection rules reveals the quantum pathways that give rise to these states. Inter-valley biexcitons identified here, comprising of neutral and charged excitons from different valleys, offer new opportunities for developing ultrathin biexciton lasers and polarization-entangled photon sources.
在原子级薄的过渡金属二卤族化合物（TMD）中，库仑相互作用的介电屏蔽减少导致强关联多体状态，包括激子和三激子，这些状态主导着光学性质。高阶态，如束缚双激子，是可能的，但使用线性光学光谱方法很难明确地识别它们。在这里，我们实施了偏振分辨二维相干光谱学（2DCS）来揭示单层 MoSe 的复杂光学响应，并确定了多个高阶相关态。中性和带电的谷间双激子的决定性特征在交叉偏振二维光谱中以各自约 20 和 5 meV 的结合能出现的不同共振出现，这与最近使用变分和蒙特卡罗方法的计算结果相似。考虑到光的谷依赖性选择定则的理论模型揭示了导致这些状态的量子途径。这里确定的谷间双激子，由来自不同谷的中性和带电激子组成，为开发超薄双激子激光和偏振纠缠光子源提供了新的机会。
