Regensburg 2025 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 55: Graphene and 2D Materials (joint session TT/HL)

HL 55.10: Vortrag

Donnerstag, 20. März 2025, 17:30–17:45, H33

Magnetism in monolayer graphene near 1/4 doping — •Maxime Lucas, Andreas Honecker, and Guy Trambly de Laissardière — Laboratoire de Physique Théorique et Modélisation, CY Cergy Paris Université / CNRS, France

Recent studies of twisted bilayer graphene (or other 2D materials) have been stimulated by the discovery of correlations between electronic flat-band states due to a moiré pattern [1]. It is shown experimentally and theoretically that the filling of the flat bands affects their magnetic properties significantly. On the other hand, the effect of doping on a simple graphene layer is still unclear. Indeed, its half-filled case is well known [2], but unlike other lattices [3] its magnetic properties beyond half filling are mostly unexplored, except at 1/4 doping [4]. Here, we present our analysis of graphene magnetism using a combination of the Hubbard model and Hartree-Fock mean-field theory. We work at density values around 1/4 doping (average number of electron per site N_e=0.75) as it puts the system right into one of the Van Hove singularities found in graphene’s density of states, giving rise to interesting magnetic properties. We present an interaction-density phase diagram and its associated magnetic orders, described by their band structure and spin structure factor.

[1] Y. Cao et al., Nature 556, 43 (2018); Nature 556, 80 (2018).

[2] M. Raczkowski et al., Phys. Rev. B 101, 125103 (2020), and Refs. therein.

[3] R. Scholle et al., Phys. Rev. B 108, 035139 (2023).

[4] S. Jiang, A. Mesaros, Y. Ran, Phys. Rev. X 4, 031040 (2014).

Keywords: Graphene; Magnetism; Hubbard model; Van Hove singularity; Real-space Mean-field