Urban Seifert

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Strong interactions between electrons can give rise to highly unconventional "quantum" phases of matter. In recent years, two-dimensional van der Waals materials have emerged as a new platform for realizing and investigating such states, with a great degree of experimental control.
In the first part of my talk, I will introduce moiré heterostructures of semiconducting transition metal dichalcogenides. In these systems, at fractional fillings, Mott-insulating states with a concomitant formation of charge crystals have been observed experimentally. I will discuss how these may serve as a platform for realizing unconventional magnetic states, in particular gapless spin liquids, and possible experimental signatures.
In the second part of my talk, I will focus on optical pump-probe spectroscopy as a tool for investigating collective excitations in van der Waals materials, and describe theoretical
models of the optical excitation and subsequent relaxation processes.
I will conclude by describing ongoing work in my group at the University of Cologne.

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Institute for Theoretical Physics, University of Cologne
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Contact: Matteo Rizzi