Edge Disorder in Bottom-Up Zigzag Graphene Nanoribbons: Implications for Magnetism and Quantum Electronic Transport

TL;DR

This study investigates how edge defects in bottom-up zigzag graphene nanoribbons influence their magnetic and electronic properties, revealing that specific missing units create spin centers and significantly affect conductance.

Contribution

It provides a detailed analysis of edge disorder effects on magnetism and transport in bottom-up graphene nanoribbons using microscopy and first-principles calculations.

Findings

Edge-missing m-xylene units are common defects.

'Bite' defects induce spin-1 paramagnetic centers.

Conductance is more affected by defects at zigzag edges.

Abstract

We unveil the nature of the structural disorder in bottom-up zigzag graphene nanoribbons along with its effect on the magnetism and electronic transport on the basis of scanning probe microscopies and first-principles calculations. We find that edge-missing m-xylene units emerging during the cyclodehydrogenation step of the on-surface synthesis are the most common point defects. These "bite'' defects act as spin-1 paramagnetic centers, severely disrupt the conductance spectrum around the band extrema, and give rise to spin-polarized charge transport. We further show that the electronic conductance across graphene nanoribbons is more sensitive to "bite" defects forming at the zigzag edges than at the armchair ones. Our work establishes a comprehensive understanding of the low-energy electronic properties of disordered bottom-up graphene nanoribbons.