RESUMO
We show here that potential barriers, applied to armchair nanoribbons, induce a hexagonal effective lattice, polarized in pseudospin on the sides of the barriers system, which has an effective unit cell greater than that of infinite graphene (pseudospin superstructure). This superstructure is better defined with the increase of the barrier potential, until a transport gap is generated. The superstructure, as well as the induced gap, are fingerprints of Kekulé distortion in graphene, so here we report an analogous effect in nanoribbons. These effects are associated with a breakdown of the chiral correlation. As a consequence, an effective zigzag edge is induced, which controls the electronic transport instead of the original armchair edge. With this, confinement effects (quasi-bound states) and couplings (splittings), both of chiral origin (decorrelation between chiral counterparts), are observed in the conductance as a function of the characteristics of the applied barriers and the number of barriers used. In general, the Dirac-like states in the nanoribbon can form quasi-bound states within potential barriers, which explains the Klein tunneling in armchair nanoribbons. On the other hand, for certain conditions of the barriers (widthLand potentialV) and the energy (E) of the quasi-particle, quasi-bound states between the barriers can be generated. These two types of confinement would be generating tunneling peaks, which are mixed in conductance. In this work we make a systematic study of conductance as a function ofE,LandVfor quantum dots systems in graphene nanoribbons, to determine fingerprints of chirality: line shapes and behaviors, associated with each of these two contributions. With these fingerprints of chirality we can detect tunneling through states within the barriers and differentiate these from tunneling through states formed between the barriers or quantum dot. With all this we propose a technique, from conductance, to determine the spatial region that the state occupies, associated with each tunneling peak.
RESUMO
The cloaking effect of electronic states was only reported in bilayer graphene. Here in this work we show that this effect can also be induced in armchair graphene nanoribbons (AGNRs), by potential barriers that modulate the chirality property of the system (correlation between pseudospins). These barriers manipulate the chirality and generates pseudospin polarizations on the sides of the barrier, which leaves spatial regions in evidence, in which states behave differently. In AGNRs the extended states (ES), associated with the tunneling of Klein, use only some sites in the nanoribbon lattice (sublattice of ES). On the other hand, the barrier applied in the nanoribbon, induces states totally localized within the region of the barrier, these states use only the sites not used by the sublattice of ES. The localized states remain invisible for electronic transport for all the energies and characteristics of the barrier in the region of the first effective transport band, the same as the states are changing. This electronic cloaking effect can be suppressed by the application of a magnetic field, detecting in the conductance the previously invisible states in the form of Fano resonances. We discuss here the possibility of using this cloaking effect to generate mechanisms that can hide information or to activate hidden system effects.
RESUMO
In this work we study some applications for pseudo-spin filters. The filters are potential barriers with hyperboloid sub-band contributions that are locally applied over graphene nano-ribbons. These filters modulate the pseudo-spin and the quirality of the wave-function allowing the recovery of the conductance loss due to imperfections, bends, or constrictions (asymmetries) found in the system. The recovery of the conductance is fulfilled by a direct manipulation of the pseudo-spin polarization at both sides of the device by localizing the filters at the system's entrance and exit points. This procedure allows the recovery of the wave-function symmetry at these points with the consequent recovery of the conductance, even when it is zero, regardless of the different internal regions that affect the transmission, i.e. the filters are used as patches for damaged regions. Our results can be extrapolated for spatially asymmetrical potentials generated by electrical (or magnetic) impurities.
RESUMO
We found that with an increase of the potential barrier applied to metallic graphene ribbons, the Klein tunneling current decreases until it is totally destroyed and the pseudo-spin polarization increases until it reaches its maximum value when the current is zero. This inverse relation disfavors the generation of polarized currents in a sub-lattice. In this work we discuss the pseudo-spin control (polarization and inversion) of the Klein tunneling currents, as well as the optimization of these polarized currents in a sub-lattice, using potential barriers in metallic graphene ribbons. Using density of states maps, conductance results, and pseudo-spin polarization information (all of them as a function of the energy V and width of the barrier L), we found (V, L) intervals in which the polarized currents in a given sub-lattice are maximized. We also built parallel and series configurations with these barriers in order to further optimize the polarized currents. A systematic study of these maps and barrier configurations shows that the parallel configurations are good candidates for optimization of the polarized tunneling currents through the sub-lattice. Furthermore, we discuss the possibility of using an electrostatic potential as (i) a pseudo-spin filter or (ii) a pseudo-spin inversion manipulator, i.e. a possible latticetronic of electronic currents through metallic graphene ribbons. The results of this work can be extended to graphene nanostructures.