Dynamical Signatures of Edge-State Magnetism on Graphene Nanoribbons

TL;DR

This study explores the magnetic properties of graphene nanoribbons' edges, revealing short-range correlations that strengthen with width, and identifies signatures of edge magnetism detectable via scanning tunneling microscopy.

Contribution

It combines quantum Monte Carlo simulations and mean-field theory to analyze edge-state magnetism, providing new insights into magnetic correlations and spectral features in graphene nanoribbons.

Findings

Correlation length increases with ribbon width.

Presence of a low-energy peak in local spectral function.

Linearly dispersing magnonlike mode at the edge.

Abstract

We investigate the edge-state magnetism of graphene nanoribbons using projective quantum Monte Carlo simulations and a self-consistent mean-field approximation of the Hubbard model. The static magnetic correlations are found to be short ranged. Nevertheless, the correlation length increases with the width of the ribbon such that already for ribbons of moderate widths we observe a strong trend towards mean-field-type ferromagnetic correlations at a zigzag edge. These correlations are accompanied by a dominant low-energy peak in the local spectral function and we propose that this can be used to detect edge-state magnetism by scanning tunneling microscopy. The dynamic spin structure factor at the edge of a ribbon exhibits an approximately linearly dispersing collective magnonlike mode at low energies that decays into Stoner modes beyond the energy scale where it merges into the particle-hole continuum.