Electronic structure of vertically coupled quantum dot-ring heterostructures under applied electromagnetic probes. A finite-element approach.

We theoretically investigate the electron and hole states in a semiconductor quantum dot-quantum ring coupled structure, inspired by the recent experimental report by Elborg and collaborators (2017). The finite element method constitutes the numerical technique used to solve the three-dimensional effective mass equation within the parabolic band approximation, including the effects of externally applied electric and magnetic fields. Initially, the features of conduction electron states in the proposed system appear discussed in detail, under different geometrical configurations and values of the intensity of the aforementioned electromagnetic probes. In the second part, the properties of an electron-hole pair confined within the very kind of structure reported in the reference above are investigated via a model that tries to reproduce as close as possible the developed profile. In accordance, we report on the energies of confined electron and hole, affected by the influence of an external electric field, revealing the possibility of field-induced separate spatial localization, which may result in an indirect exciton configuration. In relation with this fact, we present a preliminary analysis of such phenomenon via the calculation of the Coulomb integral.

1,4-Dithiolbenzene, 1,4-dimethanediolbenzene and 4-thioacetylbiphenyl molecular systems: electronic devices with possible applications in molecular electronics.

A theoretical study of the electronic transport properties of the 1,4-dithiolbenzene, 1,4-dimethanediolbenzene and 4-thioacetylbiphenyl molecules coupled to two metal contacts is carried out. The tight binding Hamiltonian approximation is applied to describe each of the molecular systems using the real space renormalization analytical method. Using Green's functions with the Landauer formalism, the transmission probability, current, shot noise and Fano factor of these three systems are calculated and analyzed in order to identify their behavior as insulators, semiconductors, or conductors, and their possible applications, such as quantum wires. The theoretical results are compared with experimental results that have been reported in the literature. The results indicate a high concordance between the results obtained by the proposed method and the experimental results.

Aromatic molecules as spintronic devices.

In this paper, we study the spin-dependent electron transport through aromatic molecular chains attached to two semi-infinite leads. We model this system taking into account different geometrical configurations which are all characterized by a tight binding Hamiltonian. Based on the Green's function approach with a Landauer formalism, we find spin-dependent transport in short aromatic molecules by applying external magnetic fields. Additionally, we find that the magnetoresistance of aromatic molecules can reach different values, which are dependent on the variations in the applied magnetic field, length of the molecules, and the interactions between the contacts and the aromatic molecule.

An array of quantum dots as a spin filter device by using Dicke and Fano effects.

In this paper we propose a new design of a spin-dependent polarizer based on a quantum dot array coupled to leads. By lifting the spin degeneracy of the carriers in the quantum dots by means of a magnetic field, Fano and Dicke effects may be used as effective means to generate spin-polarized currents. A detailed analysis of the spin-dependent transmission and polarized current as a function of the applied magnetic field and gate voltages is carried out.

Trapping and motion of polarons in weakly disordered DNA molecules.

Polaron effects for charge migration in DNA molecules have been previously considered within the Peyrard-Bishop-Holstein model. When a uniform electric field is applied, the polaron moves asymptotically at a constant velocity, provided dissipative effects are taken into account, and then current flows through DNA. Disorder originating from interactions with a random environment of solute molecules and ions surrounding the DNA molecule could prevent charge migration due to the localization of the carrier wavefunction. We studied numerically the Peyrard-Bishop-Holstein model when the disordered DNA molecule is subjected to a uniform electric field. We found the threshold value of the electric field to observe polaron motion when disorder is present. We also calculated the fluctuations of the electric current and found that they provide valuable information about the polaron dynamics.