Institute of Applied Physics and Wüzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, 01062 Dresden, Germany.
Department of Physics, University of Regensburg, 93053 Regensburg, Germany.
Nano Lett. 2023 Jun 14;23(11):4708-4715. doi: 10.1021/acs.nanolett.2c03796. Epub 2023 May 23.
Propagation of light-emitting quasiparticles is of central importance across the fields of condensed matter physics and nanomaterials science. We experimentally demonstrate diffusion of excitons in the presence of a continuously tunable Fermi sea of free charge carriers in a monolayer semiconductor. Light emission from tightly bound exciton states in electrically gated WSe monolayer is detected using spatially and temporally resolved microscopy. The measurements reveal a nonmonotonic dependence of the exciton diffusion coefficient on the charge carrier density in both electron and hole doped regimes. Supported by analytical theory describing exciton-carrier interactions in a dissipative system, we identify distinct regimes of elastic scattering and quasiparticle formation determining exciton diffusion. The crossover region exhibits a highly unusual behavior of an increasing diffusion coefficient with increasing carrier densities. Temperature-dependent diffusion measurements further reveal characteristic signatures of freely propagating excitonic complexes dressed by free charges with effective mobilities up to 3 × 10 cm/(V s).
发光准粒子的传播在凝聚态物理和纳米材料科学领域中具有核心重要性。我们在单层半导体中存在连续可调谐费米海的自由电荷载流子的情况下，实验演示了激子的扩散。通过空间和时间分辨显微镜检测到在电门控 WSe 单层中紧密结合的激子态的光发射。测量结果揭示了在电子和空穴掺杂区域中，激子扩散系数对电荷载流子密度的非单调依赖性。通过描述耗散系统中激子-载流子相互作用的分析理论，我们确定了决定激子扩散的弹性散射和准粒子形成的不同状态。交叉区域表现出随着载流子密度增加而扩散系数增加的非常不寻常的行为。温度相关的扩散测量进一步揭示了由自由电荷载流子修饰的自由传播激子复合物的特征特征，有效迁移率高达 3×10cm/（V s）。
