P. A. Orellana

TRANSPORT THROUGH A QUANTUM WIRE WITH A SIDE QUANTUM-DOT ARRAY

A noninteracting quantum-dot array side coupled to a quantum wire is studied. Transport through the quantum wire is investigated by using a noninteracting Anderson tunneling Hamiltonian. The conductance at zero temperature develops an oscillating band with resonances and antiresonances due to constructive and destructive interference in the ballistic channel, respectively. Moreover, we have found an odd-even parity in the system, whose conductance vanishes for an odd number of quantum dots while it becomes 2e(2)/h for an even number. We established an explicit relation between this odd-even parity and the positions of the resonances and antiresonances of the conductivity with the spectrum of the isolated quantum-dot array.

Electronic transport through a parallel-coupled triple quantum dot molecule : Fano resonances and bound states in the continuum

In this paper we study electronic transport through a triple quantum dot molecule attached in parallel to leads in presence of a magnetic flux. We have obtained analytical expressions of the linear conductance and density of states for the molecule in equilibrium at zero temperature. As a consequence of quantum interference, the conductance exhibits one Breit-Wigner and two Fano resonances, which positions and widths are controlled by the magnetic field. Every two flux quanta, there is an inversion of roles of the bonding and antibonding states. For particular values of the magnetic flux and dot-lead couplings, one or even both Fano resonances collapse and bound states in the continuum (BICs) are formed. We examine the line broadenings of the molecular states as a function of the Aharonov-Bohm phase around the condition for the formation of BICs, finding resonances which keep extremely narrow against variations of the magnetic field. Moreover, we analyze a molecule of

Controlling Fano and Dicke effects via a magnetic flux in a two-site Anderson model

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Conductance and persistent current of a quantum ring coupled to a quantum wire under external fields

quantum dots in the absence of magnetic field, showing that certain symmetries lead to a determinate quantity of simultaneous BICs.

Transport properties of graphene nanoribbons with side-attached organic molecules

The electronic transport through a parallel double quantum-dot molecule attached asymmetrically to leads is studied under a magnetic field. We model the system by means of a non interacting two-impurity Anderson Hamiltonian. We find that the conductance shows Fano and Dicke effects that can be controlled by the magnetic flux.

Bound states in the continuum in graphene quantum dot structures

The electronic transport of a noninteracting quantum ring side coupled to a quantum wire is studied via a single-band tunneling tight-binding Hamiltonian. We found that the system develops an oscillating band with antiresonances and resonances arising from the hybridization of the quasibound levels of the ring and the coupling to the quantum wire. The positions of the antiresonances correspond exactly to the electronic spectrum of the isolated ring. Moreover, for a uniform quantum ring the conductance and the persistent current density were found to exhibit a particular odd-even parity related with the ring order. The effects of an in-plane electric field were also studied. This field shifts the electronic spectrum and damps the amplitude of the persistent current density. These features may be used to control externally the energy spectra and the amplitude of the persistent current.

Enhancement of thermoelectric efficiency and violation of the Wiedemann-Franz law due to Fano effect

In this work we address the effects on the conductance of graphene nanoribbons (GNRs) of organic molecules adsorbed at the ribbon edge. We studied the case of armchair and zigzag GNRs with quasi-one-dimensional side-attached molecules, such as linear poly-aromatic hydrocarbons and poly(para-phenylene). These nanostructures are described using a single-band tight-binding Hamiltonian and their electronic conductance and density of states are calculated within the Greens function formalism based on real-space renormalization techniques. We found that the conductance exhibits an even-odd parity effect as a function of the length of the attached molecules. Furthermore, the corresponding energy spectrum of the molecules can be obtained as a series of Fano antiresonances in the conductance of the system. The latter result suggests that GNRs can be used as a spectrograph sensor device.

Transport in random quantum dot superlattices

The existence of bound states in the continuum was predicted at the dawn of quantum mechanics by von Neumann and Wigner. In this work we discuss the mechanism of formation of these exotic states and the feasibility to observe them experimentally in symmetrical heterostructures composed by segments of graphene ribbons with different widths forming a graphene quantum dot. We identify the existence of bound states in the continuum in these graphene quantum dot systems by means of local density of states and electronic conductance calculations.

Strong spin-dependent negative differential resistance in composite graphene superlattices

We consider the thermoelectric properties of a double-quantum-dot molecule coupled in parallel to metal electrodes with a magnetic flux threading the ring. By means of the Sommerfeld expansion we obtain analytical expressions for the electric and thermal conductances, thermopower and figure of merit for arbitrary values of the magnetic flux. We neglect electronic correlations. The Fano antiresonances in transmission demand that terms usually discarded in the Sommerfeld expansion are taken into account. We also explore the behavior of the Lorenz ratio L = κ/σT, where κ and σ are the thermal and electrical conductances and T the absolute temperature, and we discuss the reasons why the Wiedemann-Franz law fails in presence of Fano antiresonances.

Fano-Rashba effect in quantum dots

We present a model based on the two-dimensional transfer matrix formalism to calculate single-electron states in a random wide-gap semiconductor quantum dot superlattice. With a simple disorder model both the random arrangement of quantum dots (configurational disorder) and the spatial inhomogeneities of their shape (morphological disorder) are considered. The model correctly describes channel mixing and broadening of allowed energy bands due to elastic electron scattering by disorder.