Coherent transport in graphene nanoconstrictions

We study the effect of a structural nanoconstriction on the coherent transport properties of otherwise ideal zigzag-edged infinitely long graphene ribbons. The electronic structure is calculated with the standard one-orbital tight-binding model and the linear conductance is obtained using the Landauer formula. We find that, since the zero-bias current is carried in the bulk of the ribbon, this is very robust with respect to a variety of constriction geometries and edge defects. In contrast, the curve of zero-bias conductance versus gate voltage departs from the (2n+1)e2∕h staircase of the ideal case as soon as a single atom is removed from the sample. We also find that wedge-shaped constrictions can present nonconducting states fully localized in the constriction close to the Fermi energy. The interest of these localized states in regards to the formation of quantum dots in graphene is discussed.

Performance limits of graphene-ribbon field-effect transistors

The performance of field effect transistors based on an single graphene ribbon with a constriction and a single back gate are studied with the help of atomistic models. It is shown how this scheme, unlike that of traditional carbon-nanotube-based transistors, reduces the importance of the specifics of the chemical bonding to the metallic electrodes in favor of the carbon-based part of device. The ultimate performance limits are here studied for various constriction and metal-ribbon contact models. In particular, we show that, even for poorly contacting metals, properly tailored constrictions can give promising values for both the on conductance and the subthreshold swing.

La reducción enunciativa: Podemos y la constricción de la voz de la multitud

La irrupción política de Podemos en el panorama mediático y electoral español ha supuesto no sólo una revolución política sino también comunicativa. El 15M significó la crisis definitiva de la hegemonía indiscutible del Modelo Difusión en política, como ya se había verificado en otros espacios de comunicación social. Con su “no nos representan”, el 15M fue ante todo un proceso de disolución enunciativa. Tras él Podemos es el único caso de un experimento de hibridación integral del Modelo Difusión y el Modelo Reticular, intentando propiciar su sinergia. El desembarco de Pablo Iglesias en la televisión resulta crucial, pues se trata de un intento de abrochar la enunciación mediático-electoral con la enunciación popular-reticular.