Magnetic edge states and coherent manipulation of graphene nanoribbons

Abstract

Graphene, a single-layer network of carbon atoms, has outstanding electrical and mechanical properties . Graphene ribbons with nanometre-scale widths (nanoribbons) should exhibit half-metallicity and quantum confinement. Magnetic edges in graphene nanoribbons have been studied extensively from a theoretical standpoint because their coherent manipulation would be a milestone for spintronic and quantum computing devices . However, experimental investigations have been hampered because nanoribbon edges cannot be produced with atomic precision and the graphene terminations that have been proposed are chemically unstable . Here we address both of these problems, by using molecular graphene nanoribbons functionalized with stable spin-bearing radical groups. We observe the predicted delocalized magnetic edge states and test theoretical models of the spin dynamics and spin-environment interactions. Comparison with a non-graphitized reference material enables us to clearly identify the characteristic behaviour of the radical-functionalized graphene nanoribbons. We quantify the parameters of spin-orbit coupling, define the interaction patterns and determine the spin decoherence channels. Even without any optimization, the spin coherence time is in the range of microseconds at room temperature, and we perform quantum inversion operations between edge and radical spins. Our approach provides a way of testing the theory of magnetism in graphene nanoribbons experimentally. The coherence times that we observe open up encouraging prospects for the use of magnetic nanoribbons in quantum spintronic devices.

Polycyclic aromatic hydrocarbons in the graphene era

“…In this regard, an early work on the selfassembly of HBC/perylene diimide dyads could help to understand the peculiar behavior of GNRs [243]. Remarkably, through the bromo-functionalized GNR, which was synthesized by cyclodehydrogenation of the same polyphenylene percursor bearing bromo groups as described above, nitronyl-nitroxide (NIT) radicals were introduced at the edges of the GNRs (177d) [244]. Spin injection from the NIT radicals into the GNR backbone was revealed by electron spin resonance spectroscopy in conjunction with spin density calculations, demonstrating the existence of magnetic edge states of such radical-functionalized GNRs.…”

“…The studies of these N-doped p-HBCs paved the way to GNRs employing pyridinic-N-centers. For example, in 2013, Bronner, Hecht and Tegeder et al [308] reported the Ndoped chevron-type GNR 245 using 4,4′-(6,11-dibromo-1,4diphenyltriphenylene-2,3-diyl)dipyridine (244) as the monomer on Au(111) surface (Figure 54(a)). Du and Feng et al [309] in 2014 revealed the precise structure of N-doped GNR 245 by high-resolution STM.…”

Spin coherence in two-dimensional materials

“…Although a NV-like spin qubit in graphite is hypothetical, we note that spin qubits have recently been realized as edge states of graphene nanoribbons. 42 We placed a spin qubit in the center of a thin diamond slab of width d or in the central layer of a n-layer graphite (see Supplementary Information) and we considered various nuclear spin concentration. We applied a magnetic field B = 0.05 T along the three-fold axis of the defect; in this direction T 2 attains its maximum value.…”

Microwave Energy Drives “On–Off–On” Spin‐Switch Behavior in Nitrogen‐Doped Graphene

“…However, it introduces disorder and sp 3 defects that restrict charge mobility and reduce the spin relaxation length . Theoretical studies indicate that while spatial confinement and edge engineering can induce the emergence of polarized spins and currents, this is most likely to occur in graphene nanoribbons below a threshold width, with a specific edge geometry or edge functionalization (e.g., graphene nanoribbons functionalized with stable spin‐bearing radical groups) . Therefore, despite its challenges, doping with n‐ or p‐type heteroatoms may be the most practical way to equip graphene with localized spins while maintaining a charge carrier concentration high enough to preserve its conductivity.…”