Addressing electron spins embedded in metallic graphene nanoribbons

Spin-hosting graphene nanostructures are promising metal-free systems for elementary quantum spintronic devices. Conventionally, spins are protected from quenching by electronic band gaps, which also hinder electronic access to their quantum state. Here, we present a narrow graphene nanoribbon substitutionally doped with boron heteroatoms that combines a metallic character with the presence of localized spin 1/2 states in its interior. The ribbon was fabricated by on-surface synthesis on a Au(111) substrate. Transport measurements through ribbons suspended between the tip and the sample of a scanning tunneling microscope revealed their ballistic behavior, characteristic of metallic nanowires. Conductance spectra show fingerprints of localized spin states in the form of Kondo resonances and inelastic tunneling excitations. Density functional theory rationalizes the metallic character of the graphene nanoribbon due to the partial depopulation of the valence band induced by the boron atoms. The transferred charge builds localized magnetic moments around the boron atoms. The orthogonal symmetry of the spin-hosting state’s and the valence band’s wave functions protects them from mixing, maintaining the spin states localized. The combination of ballistic transport and spin localization into a single graphene nanoribbon offers the perspective of electronically addressing and controlling carbon spins in real device architectures.
We gratefully acknowledge financial support from Grants PID2019-107338RB-C61, PID2019-107338RB-C62, PID2019-107338RB-C66, PID2019-110037GB-I00, and PCI2019-111933-2 and the Maria de Maeztu Units of Excellence Program CEX2020-001038-M funded by MCIN/AEI/10.13039/501100011033, the European Regional Development Fund, the European Union (EU) H2020 program through the FET Open project SPRING (Grant Agreement No. 863098), the Xunta de Galicia (Centro de Investigación de Galicia accreditation 2019–2022, ED431G 2019/03), the Dpto. Educación Gobierno Vasco (Grant Nos. PIBA-2020-1-0014, IT1246-19, and IT-1569-22) and the Programa Red Guipuzcoana de Ciencia, Tecnología e Innovación 2021 (Grant No. 2021-CIEN-000070-01. Gipuzkoa Next). The authors acknowledge the financial support received from the IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and DIPC on behalf of the Department of Education of the Basque Government.