Electrical spin manipulation in graphene nanostructures

Abstract

We propose a mechanism to drive singlet-triplet spin transitions electrically in a wide class of graphene nanostructures that present pairs of in-gap zero modes, localized at opposite sublattices. Examples are rectangular nanographenes with short zigzag edges, armchair ribbon heterojunctions with topological in-gap states, and graphene islands with sp 3 functionalization. The interplay between the hybridization of zero modes and the Coulomb repulsion leads to symmetric exchange interaction that favors a singlet ground state. Application of an off-plane electric field to the graphene nanostructure generates an additional Rashba spin-orbit coupling, which results in antisymmetric exchange interaction that mixes S = 0 and S = 1 manifolds. We show that modulation in time of either the off-plane electric field or the applied magnetic field permits performing electrically driven spin resonance in a system with very long spin-relaxation times.

Single spin localization and manipulation in graphene open-shell nanostructures

“…Such peaked steps are characteristic of Kondo-like fluctuations of the spin once the anisotropy energy has been overcome by tunneling electrons (i.e. out of equilibrium) 31–34 . The more pronounced signal for either particle tunneling (over ZZ) or for hole tunneling (over PC) indicates the spins system lies out of particle-hole symmetry point, with E F closer to the corresponding singly unoccupied or singly occupied (SO) state, respectively.…”

Inducing a topological transition in graphene nanoribbons superlattices by external strain

“…Among them, the most promising for applications are the armchair GNR, denoted as N -AGNRs, with N the number of C atoms along the width of the ribbon [17][18][19][20][21][22]. This bottom-up approach has been successfully applied to build more complex systems, [23] such as GNRs with a specific periodic modulation in their width. [24] Recently, two works by Grönig et al [25] and Rizzo et al [26] demonstrated that periodic superlattices of N -AGNR/M -AGNR (different width) host topologically protected edge states, in close analogy to the Su-Schieffer-Heeger (SSH) model of polyacetylene [27].…”

Probing local moments in nanographenes with electron tunneling spectroscopy

“…Analogously, graphene functionalized with sp 3 defects, such as atomic hydrogen, is also predicted to host zero modes with an individual electron, forming thereby a S = 1/2 defect 16,25 . Some graphene grain boundaries are also predicted to host zero modes and local moments 22,29,35,38 , as well as some interfaces between ribbons of different width 43,46 .…”

“…Thus, there is a consensus, in the theory front, that graphene local moments arise in graphene systems where sublattice imbalance is broken 3,8,12,50 , or in systems where localized states arise close to the Fermi energy, such as grain boundaries 22,29,35,38 . These local moments are predicted to have very interesting properties: a very elegant interplay between sublattice and spin polarization 8,11,13,31 , prone to electrical control 6,18,48 and electrically driven spin resonance 46 , exotic Yu-Shiba-Russinov states when proximitized by a superconductor 39 , domain walls with fractional charge 42 , and even potential for quantum computing 20 .…”

“…Progress in bottom-up on-surface synthesis 58 in ultrahigh vacuum has made it possible to synthetize graphene nanostructures such as graphene ribbons with zigzag edges [59][60][61] , expected to have edge mag-netism with antiferromagnetic correlations between opposite edges 1,6,13,21 , triangulenes with zigzag edges [62][63][64] , expected 8 to have ferromagnetic ground state, and nanoribbon heterojunctions that host localized zero modes [65][66][67] that are expected to host local moments 43,46 . Atomic manipulation of individual atomic hydrogen chemisorbed on graphene, and the resulting changes in dI/dV observed with STM, have been reported 68 and interpreted in terms of the emergence of a localized spin.…”