Magnetic moments in the presence of topological defects in graphene

TL;DR

This paper investigates how topological defects like pentagons and dislocations affect the magnetic properties of graphene, revealing that such defects can alter magnetic ground states and introduce critical Coulomb interaction thresholds.

Contribution

It demonstrates that topological defects in graphene can significantly modify magnetic behavior, challenging the predictions of Lieb's theorem in defect-free lattices.

Findings

A single pentagon can change the magnetic ground state behavior.

Critical Coulomb U values depend on defect type and arrangement.

Regions of coexistence of polarized and unpolarized states are identified.

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.