Berlin 2015 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 12: Graphene: mostly Theory (with O/TT)

HL 12.7: Vortrag

Montag, 16. März 2015, 16:30–16:45, ER 164

Phase diagram of honeycomb lattice in Iionic-Hubbard model — •Sahar Nabavi and Morad Ebrahimkhas — Department of Science, Mahabad Branch, Islamic Azad University, Mahabad 59135, Iran

Tight binding electrons on a honeycomb lattice are described by an effective Dirac theory at low energies. An alternate ionic potential (Δ) generates a single-particle gap in the spectrum. We employ the dynamical mean field theory- iterative perturbation theory (DMFT-IPT) technique, to study the effect of on-site electron correlation (U) on energy gap of a honeycomb system. For a fixed ionic potential Δ, we find that beyond a critical value U_c1(Δ) massive Dirac fermions become massed and we have gapped energy bands. Further increasing U beyond U_c2(Δ), there will be another phase transition to the Mott insulating state. Therefore the competition between the single-particle gap parameter, Δ, and the Hubbard U between U_c1(Δ)<U<U_c2(Δ) restores the semi-metallic nature. The width of the intermediate semi-metallic regime shrinks by increasing the ionic potential. However, at small values of Δ, there is a wide interval of U values for which the system remains semi-metal. The phase diagram and energy gap of the system are identified