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HL: Fachverband Halbleiterphysik

HL 19: Focus Session: Strongly Correlated Quantum States in Moire Heterostructures (joint session TT/HL/MA)

HL 19.1: Topical Talk

Dienstag, 18. März 2025, 09:30–10:00, H36

The Thermoelectric Effect and Its Natural Heavy Fermion Explanation in Twisted Bilayer and Trilayer Graphene — Dumitru Calugaru¹, Haoyu Hu², Rafael Luque Merino³, Nicolas Regnault⁴, Frank Koppens³, Dmitri K. Efetov⁵, and •Bogdan Andrei Bernevig¹ — ¹Dept of Physics, Princeton University, Princeton, USA — ²DIPC, San Sebastián, Spain — ³ICFO, Barcelona, Spain — ⁴Laboratoire de Physique de l'ENS, Paris, France — ⁵LMU Munich, Munich, Germany

We study the interacting transport properties of twisted bilayer graphene (TBG) using the topological heavy-fermion (THF) model, where TBG comprises localized, correlated f-electrons and itinerant, dispersive c-electrons. The Seebeck coefficient of TBG exhibits unconventional traits: negative values with sawtooth oscillations at positive fillings, contrasting typical band-theory expectations. This behavior arises from the dichotomy between heavy (short-lived, correlated f-electrons) and light (long-lived, dispersive c-electrons), with transport dominated by c-electrons due to their stronger dispersion and longer lifetimes. At positive integer fillings, c- (f-)electron bands govern the electron (hole) doping side, resulting in an overall negative Seebeck coefficient. Sawtooth oscillations occur near each integer filling due to gap openings. Our results underscore the importance of electron correlations and lifetime asymmetry, naturally captured by the THF model, in understanding TBG transport properties. These findings align with experiments on twisted bilayer and trilayer graphene and highlight the interplay of heavy and light carriers.

Keywords: Twisted bilayer graphene; Thermoelectric effect; Seebeck coefficien; Topological Heavy Fermion model; Superconductivity