Effective magnetic correlations in hole-doped graphene nanoflakes

Abstract

The magnetic properties of zig-zag graphene nanoflakes (ZGNF) are investigated within the framework of the dynamical mean-field theory. At half-filling and for realistic values of the local interaction, the ZGNF is in a fully compensated antiferromagnetic (AF) state, which is found to be robust against temperature fluctuations. Introducing charge carriers in the AF background drives the ZGNF metallic and stabilizes a magnetic state with a net uncompensated moment at low temperature. The change in magnetism is ascribed to the delocalization of the doped holes in the proximity of the edges, which mediate ferromagnetic correlations between the localized magnetic moments. Depending on the hole concentration, the magnetic transition may display a pronounced hysteresis over a wide range of temperature, indicating the coexistence of magnetic states with different symmetry. This suggests the possibility of achieving the electrostatic control of the magnetic state of ZGNFs to realize a switchable spintronic device.

Inducing and controlling magnetism in the honeycomb lattice through a harmonic trapping potential

“…The critical interaction strength for the onset of magnetism has been estimated to be U c ≃ 3.87t [26] via numerically exact Quantum Monte Carlo simulations of large lattices. On smaller systems with zigzag edges, an AF spin ordering establishes at the boundaries [10,12,14]. Importantly, theoretical [12] and experimental [27] evidences suggest that this edge magnetism survives up to room temperature.…”

“…On smaller systems with zigzag edges, an AF spin ordering establishes at the boundaries [10,12,14]. Importantly, theoretical [12] and experimental [27] evidences suggest that this edge magnetism survives up to room temperature. As expected, AF order is favoured in half-filled systems, for which the Hubbard interaction is more effective in localizing the carriers.…”

Realistic theory of electronic correlations in nanoscopic systems

“…However, electronic correlations due to the local Coulomb repulsion renormalize the gap, deeply influencing the transport properties of benzene molecular junctions. It is known that local electronic correlations within DMFT reduce the spectral gap in both bulk crystal [112] and nanoscopic systems [10,16] while the corresponding exact QMC solution yields Δ > Δ 0 , suggesting an important role is played by non-local spatial correlations beyond DMFT. The DΓA is able to capture all the relevant corrections beyond DMFT, and reproduces the exact self-energy, as shown in Figures 11a-11d.…”

“…[97] From a diagrammatic prospective, the DMFT can be formulated in terms of a local approximation for the one-particle fully irreducible self-energy, owing to the locality of perturbation theory in infinite dimensions [4]. DMFT has been successfully applied to model [10,16,88] as well as realistic [8,9,15,107] nanostructures. The idea behind DMFT can be systematically extended to include non-local corrections to the self-energy beyond mean-field, by considering diagrammatic approximations based on two-particle vertex functions.…”

“…2 Interface of density functional and dynamical mean field theory for the simulation of complex structures Considerable efforts have been focussed on the modelling of correlated nanoscale systems using DMFT techniques, e.g., [5][6][7][8][9][10][11][12][13][14][15][16]. Here, we describe the approach to a material realistic DMFT scheme for nanosystems which has been implemented by the authors during the course of FOR 1346, and which is particularly flexible.…”