Lapo Bogani1
University of Oxford1
Graphene ribbons with nanometer-scale widths should exhibit half-metallicity, quantum confinement and edge effects. Magnetic edges in graphene nanoribbons have undergone intense theoretical scrutiny, because their coherent manipulation would be a milestone for spintronic and quantum computing devices. Experimental investigations are however hampered by the fact that most nanoribbons do not have the required atomic control of the edges, and that the proposed graphene terminations are chemically unstable. Several questions remain unsolved: how can spins be assembled into hybrid structures at the nanoscale? What is the influence of the graphene environment on the spin? How can we create and control coherent currents in such graphene devices? Here we try to provide an answer to these questions, exploring spin-graphene interactions by using atomically-shaped magnetic materials.<br/>We first examine bottom-up shaping of molecular graphene quantum systems. We then show that, while the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. [1] We then show how graphene nanoribbons made via molecular routes can be functionalized to create almost-ideal magnetic structures to test a decade of theoretical work. We observe the predicted delocalized magnetic edge states, and comparison with a non-graphitized reference material allows clear identification of fingerprint behaviours. We then examine how these systems can be considered excellent candidates for the observation of topological states, and unconventional types of magnetism such as Stoner interactions. We quantify the spin-orbit coupling parameters, define the interaction patterns, and unravel the spin decoherence channels. Even without any optimization, the spin coherence time is in the µs range at room temperature, and we perform quantum inversion operations between edge and radical spins.[2] The use of topological engineering and quantum decoupling sequences allows pushing coherence times up to almost ms at room temperature [3].<br/>Eventually we discuss how these systems can push the limits of quantum electronic devices, showing spintronic[4] and electron-vibrational coupling effects[5], which can make them excellent emitting systems for carbon-based optical and optoelectronic devices.<br/><br/>[1] C. Cervetti et al., Nature Materials, 2016, doi:10.1038/nmat4490;<br/>[2] M. Slota et al., Nature, 2018, https://doi.org/10.1038/s41586-018-0154-7<br/>[3] F. Lombardi et al., Science 2019<br/>[4] T. Pei et al. Nature Comms 2022<br/>[5] S. Sopp et al. Nature Materials 2022.