Conductance peaks and gaps in single-electron device with the presence of electron-electron interaction - “Nonequilibrium green function approach”

Consider a single-electron transistor (SET) with a small size quantum dot (QD), where confined energy and the Coulomb interaction control the charges adding to QD. In this paper, a theoretical analysis of the relation between source-drain voltage and gate voltage has been done to define quantum-Coulomb blocked (and unblocked) diamonds for QD that has N electrons. An analytical equation for the conductance has been derived using the non-equilibrium Green function technique (NEGFT). Further, the effect of QD size and the tunnelling rate on conductance peaks and gaps have been investigated. Finally, the effect of gate voltage on conductance peaks and gaps with respect the quantum-Coulomb blocked regions has been analysed.

An Analytical Multiple-Temperature Model for Flash Laser Irradiation on Single-Layer Graphene

A Multiple-Temperature Model is proposed to describe the flash laser irradiation of a single layer of graphene. Zhukovsky’s mathematical approach is applied to solve the Fourier heat equations based upon quantum concepts, including heat operators. Easy solutions were inferred with respect to classical mathematics. Thus, simple equations were set for the electrons and phonon temperatures in the case of flash laser treatment of a single layer of graphene. Our method avoids the difficulties and extensive time-consuming nonequilibrium green function method or quantum field theories when applied in a condensed matter. Simple expressions were deduced that could prove useful for researchers.

Об особенностях электронного транспорта в наноустройстве на основе молекулы, содержащей окислительно-восстановительный центр нитроамина

Within the framework of the density functional theory in the local density approximation and the nonequilibrium Green function method (DFT + NEGF), electron transport was studied in a nanodevice consisting of a 2'-amino-4-ethynylphenyl-4'-ethynylphenyl-5'-nitro-1-benzenethiol molecule placed between gold electrodes. Current-voltage, dI/dV-characteristics, transmission spectrum and electron density of a nanodevice are calculated. It is shown that the current-voltage characteristic of the considered nanodevice in the voltage range of -0.8÷0.9 V acquires an N-shape and appears on it a section with negative differential resistance due to resonant tunneling of quasiparticles. The same changes are observed on the dI/dV-characteristic. The results obtained may be useful for calculating new promising electronic switching devices.

Enhanced Negative Nonlocal Conductance in an Interacting Quantum Dot Connected to Two Ferromagnetic Leads and One Superconducting Lead

In this paper, we investigate the electronic transport properties of a quantum dot (QD) connected to two ferromagnetic leads and one superconducting lead in the Kondo regime by means of the finite-U slave boson mean field approach and the nonequilibrium Green function technique. In this three-terminal hybrid nanodevice, we focus our attention on the joint effects of the Kondo correlation, superconducting proximity pairing, and spin polarization of leads. It is found that the superconducting proximity effect will suppress the linear local conductance (LLC) stemming from the weakened Kondo peak, and when its coupling Γ s is bigger than the tunnel-coupling Γ of two normal leads, the linear cross conductance (LCC) becomes negative in the Kondo region. Regarding the antiparallel configuration, increasing spin polarization further suppresses LLC but enhances LCC, i.e., causing larger negative values of LCC, since it is beneficial for the emergence of cross Andreev reflection. On the contrary, for the parallel configuration, with increasing spin polarization, the LLC decreases and greatly widens with the appearance of shoulders, and eventually splits into four peaks, while the LCC decreases relatively rapidly to the normal conductance.

Photon-assisted transport through a 1D-dot-graphene similar to STM model device

By using the nonequilibrium Green function method, the photon-assisted electron transport through a graphene-based device similar to STM model is studied theoretically and numerically. The device is composed of a single central site (quantum dot) modulated by an oscillating electric field, a one-dimensional quantum wire and a two-dimensional graphene sheet. Some interesting results on transmission probability and current–voltage ([Formula: see text]–[Formula: see text]) characteristics of the device are given in this paper. In the presence of an oscillating electric field, we find that besides the central two transmission peaks caused by graphene part, there appear photon-assisted peaks which are distributed on both sides of the Fermi level. The positions of the photon-assisted peaks are linear to the frequency of the oscillating electric field, and the widths of the photon-assisted peaks are relevant to the amplitude of the oscillating electric field. It is found that the current–voltage graphs exhibit step growth due to the existence of photon-assisted tunneling. We hope these results may have guidance meaning for the fabrication of optoelectronic devices.