In stark contrast to one-dimensional spin-1/2 systems, spin-1 models, as conjectured by Haldane, have a characteristic gap in their excitation spectrum. Localized to the edges of finite spin-1 chains, topologically protected spin-1/2 edge modes appear, endowing the system with a fourfold degenerate ground state. This degenerate subspace might be used to implement a singlet-triplet spin-qubit. However, manufacturing low-dimensional spin-1 systems is notoriously difficult. Typically many such chains are synthesized in organometallic compounds, involving heavy elements. In these systems inter-chain interactions and spin-orbit coupling are non-negligible, thus complicating the picture. Recently, graphene triangulene chains have been synthesized and their magnetic response has been analyzed[1], which can be considered true realizations of one-dimensional spin-1 chains.

We determined [2] the exchange bilinear and biquadratic constants of the triangulene chains by calculating two-spin rotations in the spirit of the magnetic force theorem. We then analyzed open ended chains with an odd number of triangulenes, whose edge states pair up forming a triplet ground state. We proposed three experimental approaches to trigger and control a singlet-triplet spin transition. Two of these methods are based on applying mechanical distortion to the chain. We finally showed that the transition can be controlled efficiently by the application of an electric field. 

 

[1]:  Mishra et al, Nature 598, 287 (2021)

[2]:  G Martínez-Carracedo, L Oroszlány, A García-Fuente, L Szunyogh, J Ferrer, arXiv:2207.13683 (2022)