论文标题
在原子薄的MOS $ _ {2} $中直接查看声子动力学
Direct view of phonon dynamics in atomically thin MoS$_{2}$
论文作者
论文摘要
过渡金属二甲藻单层和异质结构是高度可调的材料系统，在二维（2D）极限下为物理现象提供了出色的模型。迄今为止，大多数研究都集中在电子和电子孔对上，但声子也起着重要的作用。在这里，我们将超快电子衍射和扩散散射用于单层二硫化钼（MOS $ _ {2} $）中的时间和动量分辨率，电子 - 音波偶联（EPC），以及从单层传输单层到单层nitride（siicon nitride）（si $ _ $ __3 $ n $ n $ n $ n $ n $ n $ n $ n $ n）。光学生成的热载体导致单层中声子在$ \ sim $ 5 ps时间尺度上产生了深刻的各向异性分布。与Ab-Initio超快动力学模拟的定量比较揭示了介电筛选在弱化EPC中的重要作用。从单层到底物的热传输是随着声子系统远离平衡而发生的。虽然已知2D中的筛选会强烈影响均衡性能，但我们的发现将此理解扩展到了动态状态。
Transition metal dichalcogenide monolayers and heterostructures are highly tunable material systems that provide excellent models for physical phenomena at the two-dimensional (2D) limit. While most studies to date have focused on electrons and electron-hole pairs, phonons also play essential roles. Here, we apply ultrafast electron diffraction and diffuse scattering to directly quantify, with time and momentum resolution, electron-phonon coupling (EPC) in monolayer molybdenum disulfide (MoS$_{2}$) and phonon transport from the monolayer to a silicon nitride (Si$_3$N$_4$) substrate. Optically generated hot carriers result in a profoundly anisotropic distribution of phonons in the monolayer on the $\sim$ 5 ps time scale. A quantitative comparison with ab-initio ultrafast dynamics simulations reveals the essential role of dielectric screening in weakening EPC. Thermal transport from the monolayer to the substrate occurs with the phonon system far from equilibrium. While screening in 2D is known to strongly affect equilibrium properties, our findings extend this understanding to the dynamic regime.
