Ferromagnetic Insulator to Metal Transition in Non-Centrosymmetric Graphene Nanoribbons

TL;DR

This study demonstrates how engineering sublattice imbalance in graphene nanoribbons induces a ferromagnetic insulator state that transitions to a metal at higher temperatures, revealing new pathways for quantum material design.

Contribution

It presents the bottom-up synthesis of non-centrosymmetric GNRs with controlled zero-modes, leading to tunable magnetic and electronic phases confirmed by multiple theoretical methods.

Findings

Strong electron correlations induce ferromagnetic insulating ground state.

Temperature increase causes insulator-to-metal transition and loss of ferromagnetic order.

Theoretical calculations support experimental observations.

Abstract

Engineering sublattice imbalance within the unit cell of bottom-up synthesized graphene nanoribbons (GNRs) represents a versatile tool for realizing custom-tailored quantum nanomaterials. The interaction between low-energy zero-modes (ZMs) not only contributes to frontier bands but can form the basis for magnetically ordered phases. Here, we present the bottom-up synthesis of a non-centrosymmetric GNR that places all ZMs on the majority sublattice sites. Scanning tunneling microscopy and spectroscopy reveal that strong electron-electron correlations, leading to the Stoner magnetic instability, drive the system into a ferromagnetically ordered insulat-ing ground state featuring a sizeable band gap of Eg ~ 1.2 eV. At higher temperatures, a chemical transformation induces an insulator-to-metal transition that quenches the ferromagnetic order. Tight-binding (TB), density functional theory, and GW calculations corroborate our experimental observations. This work showcases how control over molecular symmetry, sublattice polarization, and ZM hybridiza-tion in bottom-up synthesized nanographenes can open a path to the exploration of many-body physics in rationally designed quantum materials.