Abstract:

Atomically thin layers of semiconducting transition metal dichalcogenides (TMDs) are widely used to functionalize nanodevices made of van der Waals heterostructures. A large variety of optical and transport experiments on different TMD-based systems have revealed not only tunable optoelectronic properties, but also signatures of unconventional ground states dominated by strong correlations in correspondence of half-filled flat bands.

In this talk, I discuss recent angle-resolved photoelectron spectroscopy (ARPES) experiments on heterostructures composed of twisted (and untwisted) layers of prototypical TMDs, WSe₂ and WS₂. Modeling the experimental spectral function measured on TMD homo- and hetero-bilayers, we estimate the orbital-dependent magnitude of the effective superlattice potential that supports flat bands formation at the valence band maxima (VBM). By comparing spectral function calculations with our polarization-dependent experimental data, we observe a non-trivial distribution of the ARPES spectral weights far from VBM, suggesting a complex orbital mixing in the presence of the modulating superlattice potential.

Finally, we investigate the quasiparticle dispersion of the monolayer TMD bands at the Brillouin zone center and report a qualitatively different behavior as a function of the supporting substrate. In agreement with our effective spectral function calculations, we attribute the observed discrepancies to contrasting TMD-substrate excitations.