Correlations in van der Waals [Hetero]Structures by the Spectroscopic Fingerprints of Quasiparticles and Collective Excitations

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Our joint experimental and theoretical research project focuses on correlation effects in van der Waals [hetero]structures and in particular their spectroscopic fingerprints. By combining microscopic strong and weak coupling theories with resonant inelastic light scattering spectroscopy of collective modes, we aim to shed light on the following fundamental questions: (i) How does the interplay of electron-electron and electron-phonon interaction determine emergent phenomena and ordering in van der Waals heterostructures? (ii) How robust are correlations in van der Waals heterostructures with respect to local strain, disorder, and inhomogeneities? (iii) What can be learned by the exploration of new (optical) probes unique to van der Waals heterostructures for correlated phenomena? For the last question we will identify and utilize novel experimental techniques including spectroscopies on collective charge density excitations that can provide particularly valuable information on the nature of correlations in these systems. To address these questions, we will study various systems, including TMDC heterostructures (such as MX2 with M=Mo, W) exhibiting correlated insulating states and correlated metals, graphene (moiré) multilayers with moiré-induced superconducting states, as well as "novel" interfaces involving already correlated constituent materials like Mott-Hubbard layers and magnetic layers. Methodologically our research will employ complementary theoretical methods, particularly dynamical mean field theory and weak coupling expansions (random phase approximation and functional renormalization group techniques). In order to treat electron correlations, these methods will be applied to models based on atomistic tight-binding and continuum descriptions. Additionally, ab initio estimates of electron-phonon coupling will be obtained where necessary. To connect to this from the experimental side, inelastic light scattering and optical spectroscopy of collective modes and phonons will be used to probe correlation effects. The research of this proposal will draw a more complete picture of emergent phenomena in van der Waals [hetero]structures backed by quantitative predictions in theory corroborated by experiments.