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TT: Fachverband Tiefe Temperaturen
TT 54: Graphene: Electronic structure, excitations, etc. (joint session O/TT)
TT 54.2: Vortrag
Mittwoch, 11. März 2026, 15:15–15:30, HSZ/0204
Topological obstruction in twisted bilayer graphene — Florie Mesple1, Pierre Mallet2, •Guy Trambly de Laissardière3, Clement Dutreix4, Gérard Lapertot5, Jean-Yves Veuillen2, and Vincent T. Renard5 — 1Dept. Physics, Univ. of Washington, Seattle, USA — 2CNRS, Univ. Grenoble Alpes, Inst. Néel, Grenoble, France — 3CY Cergy Paris Univ., CNRS, LPTM, Cergy-Pontoise, France — 4Univ. Bordeaux, CNRS, LOMA, Talence, France — 5Univ. Grenoble Alpes, CEA, IRIG, PHELIQS, Grenoble, France
The rich physics of magic angle twisted bilayer graphene (TBG) results from the Coulomb interactions of electrons in nearly flat bands of non-trivial topology [1]. Here [2], we perform STM/STS measurements on a moiré pattern generated in a TBG tilted by 4.3∘, focusing on a point-like defect. We observe quasi-particle interferences (QPIs) resulting from intravalley backscattering between Dirac cones of graphene layers 1 and 2. Rationalized by tight binding calculations and T-matrix theory, our work shows that the QPIs are strongly impacted by the relative chirality of the Dirac cones of layer 1 and 2 in each valley. It establishes that, within a given moiré valley, the two Dirac cones have the same electronic chirality, as expected in the usual continuum model [3]. This peculiar topology leads to a topological obstruction.
[1] B. A. Bernevig, D. K. Efetov, Physics Today 77, 38 (2024)
[2] F. Mesple, et al., arXiv:2506.08913 (2025)
[3] R. Bistritzer, A. H. MacDonald, PNAS 108, 12233 (2011)
Keywords: twisted bilayer graphene; STM; Electronic structure calculation; Topological matter