Electronic and magnetic ground states of {112} grain boundary in graphene in the extended Hubbard model

TL;DR

This paper explores the electronic and magnetic phases of a model representing a 112 grain boundary in graphene, revealing multiferroic behavior and potential spintronics applications through mean-field analysis.

Contribution

It introduces a detailed phase diagram of the extended Hubbard model on a skewed ladder, linking it to graphene grain boundaries and uncovering multiferroic properties.

Findings

Identification of various electronic phases including charge-ordered metals and insulators.

Discovery of magnetic phases such as spin density wave and ferrimagnetism.

Demonstration of multiferroicity with coexisting magnetic order and polarization.

Abstract

We study the ground state phase diagram of the extended Hubbard model in a half-filled 5/7 skewed ladder, which is topologically equivalent to a \{112\} grain boundary in graphene and related systems. Using the mean-field method, we identify various electronic and magnetic phases in the U-V plane, by calculating the site charge and spin densities. The electronic phases include partially charge-ordered metal or insulator, and fully charge-ordered insulator. The different magnetic phases of the model are non-magnet, spin density wave, spin split compensated ferrimagnet or partial antiferromagnet. Analysis of the electronic band structure reveals that the partially charge-ordered compensated ferrimagnetic phase exhibits spin polarisation, which can be quite interesting for spintronics applications. We also compute the polarisation as a function of $U$ using the Berry phase formalism and show that the system exhibits multiferroicity with coexisting compensated ferrimagnetic spin order alongside electronic polarisations.