Magnetic moments in the presence of topological defects in graphene

Abstract

We study the influence of pentagons, dislocations and other topological defects breaking the sublattice symmetry on the magnetic properties of a graphene lattice in a Hartree Fock mean field scheme. The ground state of the system with a number of vacancies or similar defects belonging to the same sublattice is known to have total spin equal to the number of uncoordinated atoms in the lattice for any value of the Coulomb repulsion U according to the Lieb theorem. We show that the presence of a single pentagonal ring in a large lattice is enough to alter this behavior and a critical value of U is needed to get the polarized ground state. Glide dislocations made of a pentagon-heptagon pair induce more dramatic changes on the lattice and the critical value of U needed to polarize the ground state depends on the density and on the relative position of the defects. We found a region in parameter space where the polarized and unpolarized ground states coexist.Comment: 5 pages, 3 figure

Effect of pressure on the magnetism of bilayer graphene

“…We observed that both types of vacancies have the same behaviour and it coincides with what happens in SLG 7 . We have considered two vacancies on the same layer and reconstructed one of them by forming a pentagonal link t p as pictorially shown in Fig.…”

“…5,6 In particular it has been shown that, when one of the vacancies inducing magnetic moments is reconstructed to form a pentagon, the critical value of the Hubbard interaction needed to reach a finite polarization increases significantly. 7 Bilayer graphene (BLG) is even more interesting than single layer graphene (SLG) under many points of view, 8 in particular for the magnetic properties. In the Bernalstacking, BLG can support two types of vacancies giving rise to unpaired atoms: these produced by removing a site having a neighbor in the adjacent layer are named β, and these coming from sites that are not connected to the other layer called α vacancies.…”

Impact of Vacancies on Diffusive and Pseudodiffusive Electronic Transport in Graphene

“…Note that we do not take into account the spin degree of freedom, because here we focus only on the interplay between sublattice symmetry and electronic transport. The role of vacancies in inducing the magnetization of graphene (widely investigated in the literature [16][17][18][19][20]) is beyond the scope of this study. The specific repartition of the vacancies among the two sublattices is a crucial aspect of our study.…”

Ion and electron irradiation-induced effects in nanostructured materials

“…The observed magnetism may originate from defects 462,463 in the graphitic network such as undercoordinated atoms, e.g., vacancies, 303,[464][465][466][467][468] interstitials, 469 carbon adatoms, 316 and atoms on the edges of graphitic nanofragments with dangling bonds either passivated with hydrogen atoms [470][471][472] or free. 471,473 Structural defects, in general, give rise to localized electronic states, a local magnetic moment, flat bands associated with defects and thus to an increase in the density of states at the Fermi level, and eventually to the development of magnetic ordering.…”