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©IOP Publishing Ltd. This work was supported by MICINN (projects Mosaico and MAT2010-17180). The authors are grateful to P A Orellana for useful discussions of the Fano effect., A new type of quantum interference device based on a graphene nanoring in which all edges are of the same type is studied theoretically. The superposition of the electron wavefunction propagating from the source to the drain along the two arms of the nanoring gives rise to interesting interference effects. We show that a side-gate voltage applied across the ring allows for control of the interference pattern at the drain. The electron current between the two leads can therefore be modulated by the side gate. The latter manifests itself as conductance oscillations as a function of the gate voltage. We study quantum nanorings with two edge types (zigzag or armchair) and argue that the armchair type is more advantageous for applications. We demonstrate finally that our proposed device operates as a quantum interference transistor with high on/off ratio., MICINN, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2012 Elsevier B.V. All rights reserved. Work in Madrid was supported by MICINN (project MAT2010- 17180). R.P.A. Lima would like to thank CAPES via project PPCPMercosul, CNPq, and FINEP (Brazilian Research Agencies) as well as FAPEAL (Alagoas State Research Agency) for partial financial support., We study theoretically the level shift of the Dirac oscillator perturbed by any sharply peaked potential approaching a surface delta potential. A Green function method is used to obtain closed expressions for all partial waves and parities., MICINN, CAPES (Brazilian Research Agency), FINEP (Brazilian Research Agency), FAPEAL (Alagoas State Research Agency), CNPq (Brazilian Research Agency), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2014 Elsevier B.V. All rights reserved. This work was supported by MICINN (projects MAT2010-17180 and FIS2009-07880), JCYL (project SA226U13) and USAL (project KBBB). C.G.-S. acknowledges financial upport from Comunidad de Madrid and European Social Foundation., We study the scattering of massless Dirac particles by oscillating barriers in one dimension. Using the Floquet theory, we find the exact scattering amplitudes for time-harmonic barriers of arbitrary shape. In all cases the scattering amplitudes are found to be independent of the energy of the incoming particle and the transmission coefficient is unity. This is a manifestation of the Klein tunneling in time-harmonic potentials. Remarkably, the transmission amplitudes for arbitrary sharply-peaked potehtials also become independent of the driving frequency. Conditions for which barriers of finite width can be replaced by sharply-peaked potentials are discussed., Ministerio de Ciencia e Innovación (MICINN), JCYL, USAL, Comunidad de Madrid, European Social Foundation, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub