Dresden 2026 – scientific programme
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O: Fachverband Oberflächenphysik
O 66: Ultrafast electron dynamics at surface and interfaces III
O 66.8: Talk
Wednesday, March 11, 2026, 17:00–17:15, TRE/MATH
Electron and exciton dynamics in large-angle twisted bilayer graphene — •Gianmarco Gatti1, Anders Mortensen1, Gesa Siemann1, Zhihao Jiang1, Alfred Jones1, Chakradhar Sahoo1, Thomas Nielsen1, Naina Kushwaha2, Jennifer Ridgen2, Søren Ulstrup1, Bruce Weaver2, Yu Zhang2, Charlotte Sanders2, Emma Springate2, Vibha Reddy3, Ulrich Starke3, and Philip Hofmann1 — 1Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark — 2Central Laser Facility, STFC Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX, UK — 3Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany
Tunable moiré superlattices naturally form in artificially stacked monolayers through control of their rotational misalignment (twist angle). In large-angle twisted bilayer graphene (TBG), orbital hybridization between the monolayer-derived π/π* bands leads to avoided crossings and the emergence of pairs of occupied and unoccupied van Hove singularities at fixed wave vectors k*. We investigate the out-of-equilibrium electron dynamics near these points in 10°-TBG using IR-pump XUV-probe time-resolved ARPES experiments. Our measurements resolve the hot electron dynamics in TBG and reveal an additional, unexpected spectral weight within the local electronic band gap at k*. This observation is consistent with the signature of a strongly bound exciton in TBG, whose formation has been attributed by recent theoretical models to a unique destructive coherence between two energy-degenerate subband resonant transitions.
Keywords: Time-resolved ARPES; Twisted bilayer graphene; Exciton; graphene; Ultrafast dynamics