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Magnetic edge states and coherent manipulation of graphene nanoribbons

We demonstrate molecular graphene nanoribbons with magnetic edges and show how to coherently control the spin properties even at room temperature. Nature 557, 691–695 (2018).

Graphene, a single-layer network of carbon atoms, has outstanding electrical and mechanical properties1. 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.

The classical and quantum dynamics of spins on gaphene

NMat1We show how the dynamics of molecular spins on graphene is strongly affected by the interaction with graphene phonons and electrons. Nature Materials 15, 164–168 (2016).

 

Controlling the dynamics of spins on surfaces is pivotal to the design of spintronic and quantum computing devices. Proposed schemes involve the interaction of spins with graphene to enable surface-state spintronics, and electrical spin-manipulation. However, the influence of the graphene environment on the spin systems has yet to be unraveled. Here we explore the spin-graphene interaction by studying the classical and quantum dynamics of molecular magnets on graphene. While the static spin response remains unaltered, the quantum spin dynamics and associated selection rules are profoundly modulated. The couplings to graphene phonons, to other spins, and to Dirac fermions are quantified using a newly-developed model. Coupling to Dirac electrons introduces a dominant quantum-relaxation channel that, by driving the spins over Villain’s threshold, gives rise to fully-coherent, resonant spin tunneling. Our findings provide fundamental insight into the interaction between spins and graphene, establishing the basis for electrical spin-manipulation in graphene nanodevices.

The intrinsic conductance and scattering processes of large-area graphene

THz spectrometerSub-Thz spectroscopy and transport measurements provide the intrinsic conductance and main scattering mechanisms of single domains of large-area graphene.

Advanced Materials 27, 2676 (2015)

Surface organization of molecular graphene nanoribbons

TOC-01We organize and deposit molecular graphene nanoribbons on functionalized Si surfaces, in a necessary step to create electronic nanodevices.

Nanoscale 7, 12807-12811 (2015)

 

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