Electronic States of Graphene Grain Boundaries

TL;DR

This paper models amorphous graphene grain boundaries, identifying stable structures that host localized zero energy states, explaining experimental observations of enhanced magnetism and density of states at boundaries.

Contribution

It introduces a new model for amorphous grain boundaries in graphene that predicts zero energy localized states, expanding understanding beyond simple dislocation models.

Findings

Stable dislocation cores carry zero energy states.

Localized zero energy states explain experimental STS peaks.

Enhanced magnetism at grain boundaries linked to these states.

Abstract

We introduce a model for amorphous grain boundaries in graphene, and find that stable structures can exist along the boundary that are responsible for local density of states enhancements both at zero and finite (~0.5 eV) energies. Such zero energy peaks in particular were identified in STS measurements [J. \v{C}ervenka, M. I. Katsnelson, and C. F. J. Flipse, Nature Physics 5, 840 (2009)], but are not present in the simplest pentagon-heptagon dislocation array model [O. V. Yazyev and S. G. Louie, Physical Review B 81, 195420 (2010)]. We consider the low energy continuum theory of arrays of dislocations in graphene and show that it predicts localized zero energy states. Since the continuum theory is based on an idealized lattice scale physics it is a priori not literally applicable. However, we identify stable dislocation cores, different from the pentagon-heptagon pairs, that do carry zero energy states. These might be responsible for the enhanced magnetism seen experimentally at graphite grain boundaries.