Dark excitons: Energetics, dynamics, transport and correlated phases

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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.