In this paper, we present magnetic properties of a finite graphene sheet with a triangle punctured vacancy, and its counterpart single-wall carbon nanotube as a rolled-up graphene sheet in the framework of the Hubbard model in the presence of an axial electric field, in order to form a comparison study between these two graphene samples. We have noticed that the tight-binding part of the Hamiltonian consists of two types of zero-energy states in the case of the graphene sheet, the strict zero-energy states, and the quasi zero-energy states. The first type takes part in a ferromagnetic coupling between the triangle edges and one edge of the rectangle graphene sheet, while the latter one has an antiferromagnetic alignment with the opposite edge of the rectangle graphene sheet. Involving the Coulomb interaction through Hubbard term, we have observed that the slope of the cluster edge states in nanotube is higher than the graphene sheet. Additionally, spin-depolarization happens in single-wall nanotube sooner than the graphene sheet by slightly increasing an axial electric field. Also, the graphene sheet is more robust than the single wall nanotube at low electric fields.
Herein, the spin‐dependent transport properties of a zigzag graphene nanoribbon (zGNR) with edges decorated with a fluoranthene group are studied. Atomically perfect zigzag edge, including phenyl‐edge functionalization, was synthesized by Ruffieux et al. in a bottom‐up chemical technique. By performing nearest‐neighbor tight‐binding model in combination with Landauer formalism and Green's function approach, as well as considering Coulomb electronic interaction computed both with density functional calculations and mean‐field approximation of the Hubbard model, the magnetic and spin‐resolved transmissions are studied. Both the model Hamiltonian and density functional theory (DFT) descriptions yield very similar results. Importantly, by generating a special supercell, three different antiferromagnetic alignments for phenyl‐edge zGNR have been calculated, which was not developed in previous studies. The results show that by adding pentagon rings on both sides of the zGNR, the conductance loses its step‐like behavior. Our structure of interest is a semiconductor with a transport gap of 0.56 eV. This kind of defective structure will enable the spin‐feature characteristic, such as spin filtering, and add the spin degree of freedom to graphene‐based logic devices.
We have performed a theoretical study on the case of transmission-type one-dimensional magnetophotonic crystals (MPCs) to establish a practical magneto-optical isolator (MOI) that operates properly even in the presence of construction errors. We have introduced a very thin MPC structure with high transmittance and a large Faraday rotation, with the capability of adjusting to a perfect MOI. A minor thickness error for the individual layers of this MOI may take it from being a perfect MOI; however, its adjustability can provide a stable operation against fabrication errors.
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