Dresden 2026 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 2: Quantum-Critical Phenomena (joint session TT/DY)
TT 2.7: Vortrag
Montag, 9. März 2026, 11:15–11:30, HSZ/0101
Potts nematic quantum phase transition in Dirac fermion systems — •Max Fornoville1,2, Kilian Fraboulet1, Michael M. Scherer3, and Laura Classen1,2 — 1Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany — 2School of Natural Sciences, Technische Universität München, 85748 Garching, Germany — 3Theoretische Physik III, Ruhr-Universität Bochum, 44801 Bochum, Germany
With the advent of 2D moiré materials, Dirac fermion models have yet again emerged as promising candidates to describe putative quantum critical points in these systems. The presence of gapless fermions provides an avenue towards criticality beyond the conventional universality classes because it profoundly alters the quantum critical behavior, also giving rise to non-Fermi liquid behavior. We investigate the onset of nematic order in Dirac systems with hexagonal symmetry. Owing to the sixfold rotational symmetry, the nematic director selects among three equivalent orientations and the associated order parameter is described by a 3-state Potts model coupled to the Dirac fermions via a Yukawa interaction. In the ordered phase, the fermions remain gapless but the Dirac points split, dynamically breaking rotational symmetry. At the mean-field level, the transition is of first order, which we demonstrate using a minimal lattice model. We further employ a functional renormalization group approach to investigate the influence of the Dirac fermions on the Potts model and the nature of the transition due to a possible fermion-induced continuous quantum critical point.
Keywords: Quantum criticality; Dirac fermions; Electronic nematicity; Functional renormalization group