Adittional levels between Landau bands due to vacancies in graphene: towards a defect engineering

We describe the effects of vacancies on the electronic properties of a graphene sheet in the presence of a perpendicular magnetic field: from a single defect to an organized vacancy lattice. An isolated vacancy is the minimal possible inner edge, showing an antidotlike behaviour, which results in an extra level between consecutive Landau levels. Two close vacancies may couple to each other, forming a vacancy molecule tuned by the magnetic field. We show that a vacancy lattice introduce an extra band in between Landau levels with localization properties that could lead to extra Hall resistance plateaus.Comment: 6 pages, 4 figures, few comments added after referees - accepted to publication in Phys. Rev.

Valley polarization effects on the localization in graphene Landau levels

Effects of disorder and valley polarization in graphene are investigated in the quantum Hall regime. We find anomalous localization properties for the lowest Landau level (LL), where disorder can induce wavefunction delocalization (instead of localization), both for white-noise and gaussian-correlated disorder. We quantitatively identify the contribution of each sublattice to wavefunction amplitudes. Following the valley (sublattice) polarization of states within LLs for increasing disorder we show: (i) valley mixing in the lowest LL is the main effect behind the observed anomalous localization properties, (ii) the polarization suppression with increasing disorder depends on the localization for the white-noise model, while, (iii) the disorder induces a partial polarization in the higher Landau levels for both disorder models.Comment: 5 pages, 6 figures, extended version, with 2 new figures adde

Inner and outer edge states in graphene rings: A numerical investigation

We numerically investigate quantum rings in graphene and find that their electronic properties may be strongly influenced by the geometry, the edge symmetries and the structure of the corners. Energy spectra are calculated for different geometries (triangular, hexagonal and rhombus-shaped graphene rings) and edge terminations (zigzag, armchair, as well as the disordered edge of a round geometry). The states localized at the inner edges of the graphene rings describe different evolution as a function of magnetic field when compared to those localized at the outer edges. We show that these different evolutions are the reason for the formation of sub-bands of edge states energy levels, separated by gaps (anticrossings). It is evident from mapping the charge densities that the anticrossings occur due to the coupling between inner and outer edge states.Comment: 8 pages, 7 figures. Figures in low resolution due to size requirements - higher quality figures on reques

Resonant tunneling through protected quantum dots at phosphorene edges

We theoretically investigate phosphorene zigzag nanorribons as a platform for constriction engineering. In the presence of a constriction at the upper edge, quantum confinement of edge protected states reveals resonant tunnelling Breit-Wigner transmission peaks, if the upper edge is uncoupled to the lower edge. Coupling between edges in thin constrictions gives rise to Fano-like and anti-resonances in the transmission spectrum of the system.Comment: 8 pages,7 figure

Bacia hidrográfica e sua relação com o ecossistema ripário.

Matas ciliares são formações florestais situadas às margens dos cursos de água e são componentes da estrutura de bacias hidrográficas. Essas comunidades florestais esempenham inúmeras funções na dinâmica de uma bacia hidrográfica e são condições básicas para a manutenção da integridade dos processos hidrológicos e ecológicos nessas unidades da paisagem. São protegidas legalmente e estudos de sua dinâmica são importantes para formar a base na gestão e planejamento dos recursos hídricos em bacias hidrográficas. Bacias Hidrográficas são exemplos de sistemas complexos, em virtude da variedade de elementos componentes e dos fluxos de interação entre estes. Em função dessa complexidade, essa região geográfica, bem delimitada, pode ser estudada aplicando-se os conceitos de ecossistema e geossistema, como estão sendo utilizados no projeto de recuperação de mata ciliar degradada do Rio São Francisco