Dark excitons: Energetics, dynamics, transport and correlated phases

我们的目的是探索二维半导体中层内、杂化和层间激子的能量学、动力学、输运性质和相关相互作用。虽然这个方向的实验研究已经很好地建立起来，但我们的项目为开放的研究问题提供了一种补充和强大的方法：在我们的初步工作中，我们开发了新一代时间和角度分辨光电发射光谱（trARPES）实验，可以应用于剥离和人工堆叠的范德瓦尔斯异质结构；亮激子和暗激子的形成和热化动力学可以在超短的时间和长度尺度上（时间55 fs，能量150 meV，动量0.04 1/A，空间分辨率500 nm）获得。在SPP中，我们将充分利用trARPES的功能来研究过渡金属二硫族化合物（TMDs）脱落异质结构中亮激子和暗激子的时空动力学。具体来说，通过调整摩尔波长（即扭转角），通过抑制六方氮化硼（hBN）解耦层的层间杂化以及通过创建局部应变梯度，我们的目标是控制激子在空间和时间上的动力学和相关相互作用。我们将重点研究三个目标：第一，我们将研究激子约束和平带物理对TMD/TMD和TMD/hBN/TMD异质结构中亮激子和暗激子形成和热化动力学的影响。其次，为了实验表征亮激子和暗激子的扩散过程，我们将监测在moir<s:1>势、hBN解耦层和局部应变梯度存在下的时空激子动力学。第三，我们将研究TMD/hBN/TMD异质结构中暗激子凝聚物的产生和稳定性。在现有的实验方法之外，我们将利用动量分辨光电发射技术和轨道层析成像技术，从激子实空间波函数的角度研究激子凝聚体。

We aim to explore the energetics, dynamics, transport properties and correlated interactions of intralayer, hybrid and interlayer excitons in two-dimensional semiconductors. While experimental research in this direction is well established, our project provides a complementary and powerful approach to open research questions: In our preliminary work, we have developed a new generation time- and angle-resolved photoemission spectroscopy (trARPES) experiment that can be applied to exfoliated and artificially stacked van-der-Waals heterostructures; the formation and thermalization dynamics of bright and dark excitons can be accessed on ultrashort time- and length-scales (55 fs time-, 150 meV energy-, 0.04 1/A momentum- and 500 nm spatial-resolution). In the SPP, we will make use of the full capabilities of trARPES to study the spatio-temporal dynamics of bright and dark excitons in exfoliated heterostructures of transition metal dichalcogenides (TMDs). Specifically, by tuning the moiré wavelength (i.e., the twist-angle), by suppressing interlayer hybridization by hexagonal boron nitride (hBN) decoupling layers and by creating local strain gradients, we aim to control the dynamics and correlated interactions of excitons in space and time. We will focus on three objectives: First (i), we will study the impact of exciton confinement and flat band physics onto the formation and thermalization dynamics of bright and dark excitons in TMD/TMD and TMD/hBN/TMD heterostructures. Second (ii), in order to experimentally characterize diffusion processes of bright and dark excitons, we will monitor the spatio-temporal exciton dynamics in the presence of the moiré potential, hBN decoupling layers and local strain gradients. And third (iii), we will investigate the creation and stabilization of dark exciton condensates in TMD/hBN/TMD heterostructures. Beyond the established experimental approaches, we will make use of momentum-resolved photoemission technique and orbital tomography in order to study exciton condensates from the perspective of the exciton’s real-space wavefunction.