We have developed a Hartree-Fock theory for electrons on a honeycomb lattice aiming to solve a long-standing problem of the Fermi velocity renormalization in graphene. Our model employs no fitting parameters (like an unknown band cutoff) but relies on a topological invariant (crystal structure function) that makes the Hartree-Fock sublattice spinor independent of the electron-electron interaction. Agreement with the experimental data is obtained assuming static self-screening including local field effects. As an application of the model, we derive an explicit expression for the optical conductivity and discuss the renormalization of the Drude weight. The optical conductivity is also obtained via precise quantum Monte Carlo calculations which compares well to our mean-field approach.
Using density functional theory, we have investigated the electronic and magnetic properties of finite-size as well as infinitely periodic organometallic vanadium-borazine systems (V n (B 3 N 3 H 6 ) n+1 for their possible applications in spintronics devices. From our calculations, we find the V n (B 3 N 3 H 6 ) n+1 systems to be structurally more stable in comparison to their isoelectronic benzene counterparts (V n (C 6 H 6 ) n+1 ). All the V n (B 3 N 3 H 6 ) n+1 systems are found to be ferromagnetically stabilized, with the infinite one-dimensional [V(B 3 N 3 H 6 )] wire exhibiting robust half-metallic behaviour. The V n (B 3 N 3 H 6 ) n+1 clusters are also found to exhibit efficient spin filter properties when coupled to graphene electrodes.
Using density functional theory, we investigate TM-cyclopentadienyl-benzene sandwich molecular wires (SMWs) which are composites of TM-cyclopentadienyl and TM-benzene wires (TM = transition metal (V, Fe)). All the SMWs are found to be highly stable ferromagnetic half-metals, showing spin switching behavior. Transport calculations show that finite size clusters display spin filter property when coupled with Au electrodes on either side. I − V b characteristics of all systems confirm the spin filter property, with Au-BzVCpVBz-Au displaying exceptionally high performance. In addition to spin filtering, the Au-BzFeCpFeBz-Au system also shows negative differential resistance (NDR). Compression causes an abrupt reduction in magnetic moment and a transition to a metallic phase, while stretching causes an increase in magnetic moment. Half-metallicity is preserved for modest amounts of stretching and compression.
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