Tuning Topological End-States in Armchair Graphene Nanoribbons
Daniel Sánchez-Portal
Centro de Física de Materiales CSIC-UPV/EHU, 20018 Donostia-San Sebastián, Spain
e-mail: daniel [dot] sanchez [at] ehu [dot] eus (daniel[dot]sanchez[at]ehu[dot]eus)
Recent advances on surface-assisted synthesis open the door to engineering topological phases in atomically precise graphene nanoribbons (GNRs). However, to fully exploit their potential, a rational design is needed to achieve GNRs with optimal properties for spintronics or quantum computing applications.
Here I will discuss the appearance and possible tuning of topological end- and interface-states in armchair GNRs (aGNRs) and heterostructures formed by aGRN segments of different widths. I will first review the conditions for the appearance of end-states in aGNRs, their number as a function of the width and termination of the ribbon, and how they evolve into interface states at aGNR-heterojunctions [1]. Then, I will discuss the manipulation of the end-states of 5-aGNR by lateral chemical functionalization [2]. The existence of end-state in 5-aGNR has been confirmed both theoretically and experimentally [3]. Given the small band gap of 5-aGNR, we might expect to be able to tune the topology of this ribbon, and thus the appearance of end-states, by several means. Here we demonstrate that decorating the ribbon with electronegative species like F or OH provides a viable route. Finally, I will present a novel family of armchair GNRs, which we name haiku-AGNRs, consisting of 5- and 7-atom wide segments. Based on ab initio simulations, we predict a tunable topological phase dependent on the density of the 7-atom wide segments, with the concomitant emergence or quenching of topological end and interface states [4]. Moreover, we derive a generalized Su-Schrieffer-Heeger (SSH) model that allows treating haiku-AGNRs of technologically relevant lengths, thus providing valuable information for the devise of future experiments. Time permitting, I will also present some results for B-doped periodic haiku-AGNRs in comparison with experiments performed at Prof. Pascual’s lab in nanoGUNE, San Sebastian (Spain) [5].
[1] S. Sanz and D. Sánchez-Portal, Predicting interface and spin states in armchair graphene nanoribbon junctions, arXiv:2507.14065
[2] D. García-Pina, A. Garcia-Lekue and D. Sánchez-Portal, in preparation.
[3] J. Lawrence et al., Probing the Magnetism of Topological End States in 5‑Armchair Graphene Nanoribbons, ACS Nano 14, 4499-4508 (2020).
[4] R. E. Menchón, P. Brandimarte, D. Sánchez-Portal, and A. Garcia-Lekue, Haiku graphene nanoribbons as novel platforms for tunable topology, submitted (2025)
[5] N. Friedrich, R. E Menchón, I. Pozo, J. Hieulle, A. Vegliante, J. Li, D. Sánchez-Portal, D. Peña, A. Garcia-Lekue and J. I. Pascual, Addressing electron spins embedded in metallic graphene nanoribbons, ACS Nano 16, 14819-14826 (2022)