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PGI-1 Talk: Prof. Dr. Alexander Grüneis

Electronic structure control of 2D matter

30 Jan 2019 11:30
PGI Lecture Hall

University of Cologne


The electronic structure of 2D matter can be controlled by chemical functionalization and the fabrication of vertical heterostructures between dissimilar 2D layers. The present talk illustrates this approach for a number of 2D materials (graphene, MoS2 and phosphorene) by employing a unique combination of ultra-high vacuum Raman/luminescence and angle-resolved photoemission spectroscopy (ARPES).
As a first example, it is shown that ionic functionalization of graphene by alkali metals enables tuning of the charge carrier density into the superconducting regime. We find a characteristic phonon frequency change with carrier concentration that is explained by the removal of the Kohn anomaly and a bond length increase upon doping. ARPES shows a “kink” feature in the pi band of graphene due to electron-phonon interaction. For ultra-large doping, we are able to shift the Fermi level beyond the van Hove singularity of graphene located in the middle of the Brillouin zone edge. The appearance of a flat band at the Fermi level is shown by ARPES and marks the Lifshitz transition in graphene.
For phosphorene, we find that chemical doping introduces a staggered potential resulting in a band inversion that is driven purely by the Coulomb interaction between individual layers [3]. Our tight-binding simulations can fully explain the observed band structure and highlight the role of glide mirror symmetry. Finally, for molecular beam epitaxy grown graphene/MoS2 heterostructures, the non-interacting nature of the two layers is shown. Surprisingly, find a narrow photoluminescence peak of MoS2 despite the metallic substrate.


Prof. Dr. Stefan Blügel
Phone: +49 2461 61-4249
Fax: +49 2461 61-2850