Project Details
Projekt
Exploring Electronic Correlations, Excitonics and Topology on Ultrafast Timescales in van der Waals Heterostructures
Applicant
Professor Dr. Ralph Ernstorfer
Subject Area
Experimental Condensed Matter Physics
Term
since 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 443366970
The present proposal builds on a previously granted project within the first funding period of the priority program. In our previous work centered on the technique of time- and angle-resolved photoelectron spectroscopy (trARPES), we channeled our efforts toward two cardinal objectives. First, we explored and expanded the information content of static and time-resolved ARPES beyond the dispersion of electron energy eigenvalues and the occupation of states toward information about the eigenfunctions and topological properties. Studying several semiconducting and semimetallic van der Waal materials, we have mapped the orbital topology of the electronic bands, retrieved dynamically the key properties of excitons including the size of their wavefunctions, expanded the concept of electronic band mapping to excited states, and demonstrated dynamical control of a Lifshitz transition. Second, we applied these approaches to heterostructures and investigated the interfacial charge and energy transfers within topologically trivial 2D interfaces such as Au/WSe2 and WSe2/graphene. The findings from these studies have offered substantial insights into the electron dynamics of such systems, laying out a solid foundation for the present research proposal. For the forthcoming funding period, we aspire to fully delve into the complexity of 2D heterostructures. We focus our interest on one type of heterointerface: the one formed by the two semiconducting transition metal dichalcogenides WSe2 and MoTe2. Overlaying monolayers of the hexagonal H phase of these materials gives rise to a moirè modulation of the potential arising from the significant lattice mismatch (~7%). This system has recently seen a surge of interest triggered by the observation of correlated emergent behavior and tunable modifications of band topology. Sometimes heralded as a “simple” tunable construction kit to produce correlated physics, this system is just beginning to be explored and it is far from being understood. The debate is open regarding how (and whether) the strongly correlated nature of the moiré bands enters topological physics. Furthermore, MoTe2 exists also in a distorted octahedral phase (Td) that is a Weyl Type-II semi-metal with non-trivial and easily perturbed band topology. It is possible to switch between the phases by electrostatic doping, laser irradiation, and strain, and the relevance of this structural transition to the phenomena observed in the heterostructure is yet to be addressed. Our goal is to use the direct insight provided by angle-resolved photoemission spectroscopy (ARPES) and time-resolved photoemission spectroscopy (tr-ARPES) to elucidate the intricate physics that has come to light in these complex layered systems. Given the latest advancements in sample preparation techniques, and our newly-developed tools to map the topology of the electronic bands, excitonic states, and charge transfer dynamics, we are well-positioned to tackle this puzzling system.
DFG Programme
Priority Programmes
Co-Investigator
Dr. Tommaso Pincelli
