Spin Excitation in Nano-Graphite Ribbons with Zigzag Edges

TL;DR

This paper theoretically investigates spin excitations in nano-graphite ribbons with zigzag edges, revealing a parity-dependent gap in the excitation spectrum due to localized edge states.

Contribution

It models the low-energy spin physics of zigzag-edged nano-graphite ribbons using an effective Heisenberg Hamiltonian and maps it to an O(3) nonlinear sigma model, highlighting a parity effect.

Findings

Spin excitation gap exists for even zigzag lines.

Gapless spin excitations occur for odd zigzag lines.

Edge state localization influences low-energy spin dynamics.

Abstract

Spin excitation in a nano-graphite ribbon with zigzag edges is investigated theoretically. Due to the strongly localized nature of the states near Fermi energy, the effective Hamiltonian for the low energy physics is given by Heisenberg Hamiltonian with the nearest neighbor exchange coupling. The action corresponding to the effective Hamiltonian is mapped to that of the O(3) nonlinear sigma model. It is shown that the spin excitation has a gap when the number of the zigzag lines is even, whereas the excitation becomes gapless in case of the odd number of the zigzag lines.