Intertwined lattice deformation and magnetism in monovacancy graphene

Abstract

Using density functional calculations we have investigated the local spin moment formation and lattice deformation in graphene when an isolated vacancy is created. We predict two competing equilibrium structures: a ground state planar configuration with a saturated local moment of 1.5 µB, and a metastable non-planar configuration with a vanishing magnetic moment, at a modest energy expense of 50 meV. Though non-planarity relieves the lattice of vacancy-induced strain, the planar state is energetically favored due to maximally localized defect states (vσ, vπ). In the planar configuration, charge transfer from itinerant (Dirac) states weakens the spin-polarization of vπ yielding a fractional moment, which is aligned parallel to the unpaired vσ electron through Hund's coupling. As a byproduct, the Dirac states (dπ) of the two sublattices undergo a minor spin-polarization and couple antiferromagnetically. In the non-planar configuration, the absence of orthogonal symmetry allows interaction between vσ and local dπ states, to form a hybridized vσ state. The non-orthogonality also destabilizes the Hund's coupling, and an antiparallel alignment between vσ and vπ lowers the energy. The gradual spin reversal of vπ with increasing non-planarity opens up the possibility of an intermediate structure with balanced vπ spin population. If such a structure is realized under external perturbations, diluted vacancy concentration may lead to vσ based spin-1/2 paramagnetism. Carrier doping, electron or hole, does not alter the structural stability. However, the doping proportionately changes the occupancy of vπ state and hence the net magnetic moment. arXiv:1605.03921v1 [cond-mat.mtrl-sci]

Tunable magnetism of a single-carbon vacancy in graphene

“…Such a result is further confirmed by our STS maps recorded at the energies of the two spin-polarized states ( Fig. 2c), revealing the site-specific spin polarization around the single-carbon vacancy, as predicted theoretically [5][6][7][8][9][10][11][12][13][14][15][16][17][18] . The above results explicitly demonstrate that the observed two peaks in the spectra are the two spin-polarized states of the V state.…”

Single vacancy defect in graphene: Insights into its magnetic properties from theoretical modeling

“…We stress however that the picture is qualitatively different when moving from the (6 × 6) to the other supercells. In the first case the bands crossing the Fermi energy, seen also in previous works [11,[14][15][16], are rather delocalized, not strictly defect-localized states. 2. (Color online)Isosurfaces for the V π, d' π and lπ defect states (indicated in Figs.…”

Gate-dependent vacancy diffusion in graphene

“…The Jahn-Teller (JT) distorted planer vacancy with 5-9 ring structure V 1 (5|9) and one unsaturated dangling bond is found to be the ground state with 7.65 eV formation energy, which is in agreement with the previous theoretical and experimental results. [16,18,44] The other JT distorted vacancy structure V 1 is found to be metastable with 0.2 eV higher energy. Further details are in Supplemental Material.…”