Carlos Paez

Robust signatures in the current–voltage characteristics of DNA molecules oriented between two graphene nanoribbon electrodes

In this work, we numerically calculate the electric current through three kinds of DNA sequences (telomeric, λ-DNA and p53-DNA) described by different heuristic models. A bias voltage is applied between two zigzag edged graphene contacts attached to the DNA segments, while a gate terminal modulates the conductance of the molecule. Calculation of the current is performed by integrating the transmission function (calculated using the lattice Greens function) over the range of energies allowed by the chemical potentials. We show that a telomeric DNA sequence, when treated as a quantum wire in the fully coherent low-temperature regime, works as an excellent semiconductor. Clear steps are apparent in the current–voltage curves of telomeric sequences and are present independent of length and sequence initialization at the contacts. We also find that the molecule–electrode coupling can drastically influence the magnitude of the current. The difference between telomeric DNA and other DNAs, such as λ-DNA and DNA for the tumour suppressor p53, is particularly visible in the length dependence of the current.

Disorder effect on the anisotropic resistivity of phosphorene determined by a tight-binding model

In this work we develop a compact multi-orbital tight-binding model for phosphorene that accurately describes states near the main band gap. The model parameters are adjusted using as reference the band structure obtained by a density-functional theory calculation with the hybrid HSE06 functional. We use the optimized tight-binding model to study the effects of disorder on the anisotropic transport properties of phosphorene. In particular, we evaluate how the longitudinal resistivity depends on the lattice orientation for two typical disorder models: dilute scatterers with high potential fluctuation amplitudes, mimicking screened charges in the substrate, and dense scatterers with lower amplitudes, simulating weakly bounded adsorbates. We show that the intrinsic anisotropy associated to the band structure of this material, although sensitive to the type and intensity of the disorder, is robust.

Current flow in biased bilayer graphene: the role of sublattices

We investigate here how the current flows over a bilayer graphene in the presence of an external electric field perpendicularly applied (biased bilayer). Charge density polarization between layers in these systems is known to create a layer pseudospin, which can be manipulated by the electric field. Our results show that current does not necessarily flow over regions of the system with higher charge density. Charge can be predominantly concentrated over one layer, while current flows over the other layer. We find that this phenomenon occurs when the charge density becomes highly concentrated over only one of the sublattices, as the electric field breaks layer and sublattice symmetries for a Bernal-stacked bilayer. For bilayer nanoribbons, the situation is even more complex, with a competition between edge and bulk effects for the definition of the current flow. We show that, in spite of not flowing trough the layer where charge is polarized to, the current in these systems also defines a controllable layer pseudospin.

Zigzag phosphorene nanoribbons: one-dimensional resonant channels in two-dimensional atomic crystals

We theoretically investigate phosphorene zigzag nanoribbons as a platform for constriction engineering. In the presence of a constriction at one of the edges, quantum confinement of edge-protected states reveals conductance peaks, if the edge is uncoupled from the other edge. If the constriction is narrow enough to promote coupling between edges, it gives rise to Fano-like resonances as well as antiresonances in the transmission spectrum. These effects are shown to mimic an atomic chain like behavior in a two dimensional atomic crystal.

Electronic localization at mesoscopic length scales: different definitions of localization and contact effects in a heuristic DNA model

In this work we investigate the electronic transport along model disordered DNA molecules using an effective tight-binding approach, addressing the localization properties. Different tools to investigate the degree of localization are examined as a function of system length, energy dependence and DNA to electrode coupling: localization length, participation number and sensitivity to boundary conditions. Combining the results obtained from these different tools, a thermodynamic limit for the model DNA molecule, within the mesoscopic length scale, can be established. Furthermore, three aspects are investigated: (i) the influence of strongly localized resonances on the localization length is discussed as an important mechanism defining the degree of localization for sizes below the thermodynamic limit; (ii) the dependence on the Hamiltonian parameters on a possible diffusive regime for short systems; and, finally, (iii) possible length dependent origins for the large discrepancies among experimental results for the electronic transport in DNA samples.

Delocalization of vibrational normal modes in double chains: Application to DNA systems

In this work we investigate the localization of normal modes for several heuristic models of DNA like chains. The main finding is a possible robust normal mode delocalization in a finite low frequency range, irrespective of sequencing.