Out of equilibrium transport in quantum dots structures


Book Description

Neste trabalho estudamos as propriedades eletrônicas e de transportede uma molécula artificial diatômica que consiste de dois pontos quânticosconectados a dois contatos submetidos a um potencial externo. Cada pontoquântico é descrito por um nível de energia no qual os elétrons estãofortmente correlacionados pela interação Coulombiana no interior e entreos pontos quânticos. Duas topologias são consideradas para o sistema:uma corresponde aos dois pontos dispostos numa linha de condução e ooutro a uma configuração em paralelo. O problema é tratado com asfunções de Green obtidas a partir do formalismo de Keldysh para o sistemafora do equilíbrio. Estas funções permitem o cálculo da carga nos pontosquânticos e da corrente elétrica no sistema. A física do sistema é controladaprincipalmente pelas várias interações Coulombianas. Para a configuraçãoem paralelo existem dois canais interferindo para a propagação do elétronpelo sistema, cujas propriedades dependem do estado de carga de cadaponto quântico. Para a configuração em série a corrente é controlada pelapossibilidade da carga ser drenada de um ponto quântico ao outro. O estadode carga em cada ponto quântico e a corrente elétrica são discutidos emdetalhe para as duas configurações e para diferentes valores dos parâmetrosque definem o sistema.




Non-Equilibrium Quantum Dots: Transport


Book Description

The electronic transport through three-dimensionally confined semiconductor quantum dots is investigated and analyzed. The spectrum corresponds to resonant tunneling from laterally confined emitter contact subbands through the discrete three-dimensionally confined quantum dot states. Momentum non-conservation is observed in these structures.










Nonequilibrium Electron Transport in Quantum Dot and Quantum Point Contact Systems


Book Description

Much experimental research has been performed in the equilibrium regime on individual quantum dots and quantum point contacts (QPCs). The focus of the research presented here is electron transport in the nonequilibrium regime in coupled quantum dot and QPC systems fabricated on AlGaAs/GaAs material using the split gate technique. Near equilibrium magnetoconductance measurements were performed on a quantum dot and a QPC. Oscillations were seen in the conductance of the sensor which corresponded to Aharonov-Bohm oscillations in the quantum dot, to our knowledge the first such observation. Sudden jumps in the conductance of the QPC were observed under certain gate biases and under certain magnetic fields. When the gate biases and magnetic field were held constant and the conductance was observed over time, switching was observed with the form of a random telegraph signal (RTS). RTS switching is usually attributed to charging of a single impurity. However, in this case switching may have been due to tunneling via edge states in the dot. Nonequilibrium transport in single quantum dots was investigated. A knee or kink was observed in the current-voltage characteristics of two dots on different material. The bias conditions under which the knee occurred point to electron heating as the physical mechanism for the observed behavior. However, the data can not be fit accurately over all bias ranges with an energy balance hot electron model. Modifications to the model are needed to accurately represent the devices studied here. Finally, the effect of nonlinear transport through a one dimensional (1D) QPC on the equilibrium conductance of an adjacent OD quantum dot was explored. This was the first attempt to observe Coulomb drag between a OD and 1D system. It was observed that the equilibrium conductance peaks in the quantum dot were broadened as the current in the QPC increased. This apparent electron heating effect in the dot can be explained by a simple ballistic phonon model. However, reasonable phase coherence times can be estimated from peak fitting using a Breit- Wigner formula which points to a Coulomb interaction. More detailed numerical calculations should illuminate the dominant scattering processes.




Quantum Dots Handbook


Book Description

This book gives innovative and resourceful techniques for calculating the optical and transport characteristics of quantum dot structures. The book deals with the importance of transport and electronic characteristics of quantum dot structures. This is a collaborative initiative, providing primary research such as the ones conducted in physics, chemistry, and material science. This book serves as a source of reference for this field.




Electron Transport in Quantum Dots


Book Description

When I was contacted by Kluwer Academic Publishers in the Fall of 200 I, inviting me to edit a volume of papers on the issue of electron transport in quantum dots, I was excited by what I saw as an ideal opportunity to provide an overview of a field of research that has made significant contributions in recent years, both to our understanding of fundamental physics, and to the development of novel nanoelectronic technologies. The need for such a volume seemed to be made more pressing by the fact that few comprehensive reviews of this topic have appeared in the literature, in spite of the vast activity in this area over the course of the last decade or so. With this motivation, I set out to try to compile a volume that would fairly reflect the wide range of opinions that has emerged in the study of electron transport in quantum dots. Indeed, there has been no effort on my part to ensure any consistency between the different chapters, since I would prefer that this volume instead serve as a useful forum for the debate of critical issues in this still developing field. In this matter, I have been assisted greatly by the excellent series of articles provided by the different authors, who are widely recognized as some of the leaders in this vital area of research.




Transport in Nanostructures


Book Description

The advent of semiconductor structures whose characteristic dimensions are smaller than the mean free path of carriers has led to the development of novel devices, and advances in theoretical understanding of mesoscopic systems or nanostructures. This book has been thoroughly revised and provides a much-needed update on the very latest experimental research into mesoscopic devices and develops a detailed theoretical framework for understanding their behaviour. Beginning with the key observable phenomena in nanostructures, the authors describe quantum confined systems, transmission in nanostructures, quantum dots, and single electron phenomena. Separate chapters are devoted to interference in diffusive transport, temperature decay of fluctuations, and non-equilibrium transport and nanodevices. Throughout the book, the authors interweave experimental results with the appropriate theoretical formalism. The book will be of great interest to graduate students taking courses in mesoscopic physics or nanoelectronics, and researchers working on semiconductor nanostructures.




Low Temperature Transport Through a Quantum Dot: the Anderson Model Out of Equilibrium


Book Description

The infinite-U Anderson model is applied to non-equilibrium transport through a quantum dot containing two spin levels weakly coupled to two leads. At low temperatures, the Kondo peak in the equilibrium density of states is split upon the application of a voltage bias. The split peaks, one at the chemical potential of each lead, are suppressed by non-equilibrium dissipation. In a magnetic field, the Kondo peaks shift away from the chemical potentials by the Zeeman energy, leading to an observable peak in the differential conductance when the non-equilibrium bias equals the Zeeman energy. Infinite-U Anderson model, Kondo peak, Zeeman energy, Low-temperature transport through a quantum dot, Kondo effect.




Quantum Dots: Optical Properties


Book Description

This book gives innovative and resourceful techniques for calculating the optical and transport characteristics of quantum dot structures. The book has important chapters which discuss the novel optical properties of quantum dot structures. This is a collaborative book, providing primary research such as the ones conducted in physics, chemistry and material science. This book serves as an important source of reference for this field.