Robust band gap and half-metallicity in graphene with triangular perforations

Abstract

Ideal graphene antidot lattices are predicted to show promising band gap behavior (i.e., E G 500 meV) under carefully specified conditions. However, for the structures studied so far this behavior is critically dependent on superlattice geometry and is not robust against experimentally realistic disorders. Here we study a rectangular array of triangular antidots with zigzag edge geometries and show that their band gap behavior qualitatively differs from the standard behavior which is exhibited, e.g., by rectangular arrays of armchair-edged triangles. In the spin unpolarized case, zigzag-edged antidots give rise to large band gaps compared to armchair-edged antidots, irrespective of the rules which govern the existence of gaps in armchair-edged antidot lattices. In addition the zigzag-edged antidots appear more robust than armchair-edged antidots in the presence of geometrical disorder. The inclusion of spin polarization within a mean-field Hubbard approach gives rise to a large overall magnetic moment at each antidot due to the sublattice imbalance imposed by the triangular geometry. Half-metallic behavior arises from the formation of spin-split dispersive states near the Fermi energy, reducing the band gaps compared to the unpolarized case. This behavior is also found to be robust in the presence of disorder. Our results highlight the possibilities of using triangular perforations in graphene to open electronic band gaps in systems with experimentally realistic levels of disorder, and furthermore, of exploiting the strong spin dependence of the system for spintronic applications.

Electron trajectories and magnetotransport in nanopatterned graphene under commensurability conditions

“…A major issue is the deterioration of the graphene sheet quality and the difficulty in maintaining a uniform size and separation of antidots throughout the lattice. Indeed, the band-gap behavior predicted for certain lattice geometries [23,24,[38][39][40][41][42][43][44][45] is particularly sensitive to small levels of geometric disorder, which may not be possible to eliminate in experiment [46][47][48][49][50][51]. Although such uniformity is not an essential ingredient for commensurability oscillations, invasive etching processes usually reduce the mean free path significantly so that electrons are principally scattered by defects and not antidots, thus suppressing commensurability effects.…”

Nanostructured graphene for spintronics

“…The weak intrinsic spin-orbit coupling and long spin diffusion lengths suggest graphene as an ideal spintronic material [1][2][3][4][5][6][7][8][9][10]. Spin splitting or filtering in graphene is predicted for half-metallic nanoribbons [2,[11][12][13] [24][25][26], and, in particular, nanostructured zigzag (zz)-edged devices [11][12][13]15,16,[27][28][29][30][31][32][33] are among the proposed graphene-based half metals. Spin filters have been proposed using triangular dots [15,31] or perforations [29] with many similarities, e.g., low-energy localized magnetic states and a net sublattice imbalance.…”

“…The zz-edged structures support local ferromagnetic moments [3], however, global ferromagnetism is induced when the overall sublattice symmetry of the edges is broken [11][12][13]16,27,28,45]. This occurs for zzedged triangles [15,[29][30][31][32][33]. We have recently discussed the electronic structure of triangular graphene antidot lattices (GALs) [33]-here, we focus on transport through devices…”

“…Half-metallic systems are excellent platforms for manipulating spin due to their inherent spin filtering behavior. Self-assembled organometallic frameworks [22] and graphene-boron-nitride structures [23], point defects and hydrogenation [24][25][26], and, in particular, nanostructured zigzag (zz)-edged devices [11][12][13]15,16,[27][28][29][30][31][32][33] are among the proposed graphene-based half metals. Spin filters have been proposed using triangular dots [15,31] or perforations [29] with many similarities, e.g., low-energy localized magnetic states and a net sublattice imbalance.…”

“…This occurs for zzedged triangles [15,[29][30][31][32][33]. We have recently discussed the electronic structure of triangular graphene antidot lattices (GALs) [33]-here, we focus on transport through devices * sorgre@nanotech.dtu.dk containing a small number of antidots. Our calculations show that large spin-polarized currents are generated by the device illustrated in Fig.…”