Transporte eletrônico de carga e spin em cadeias de pontos quânticos

• Autor(a) principal: Coutinho, Renato Máximo
• Data de Publicação: 2013
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UFU
• Texto Completo: https://repositorio.ufu.br/handle/123456789/15665
• topic: Transporte eletrônico; Pontos quânticos; Funções de Green; Corrente elétrica; Shot noise; Electronic transport; Quantum dots; Green s functions; Electrical current; Shotnoise; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA

In the present work we investigate theoretically the quantum transport in both, stationary and transient regimes of system composed of the two quantum dots coupled to each other via hopping and to reservoirs. Using nonequilibrium Green function technique we calculate spinresolved current and ocupation in the presence of ferromagnetic leads. The analysis of the shot noise was also carried out, observing effects on both zero frequency and also finite frequency. In particular, for the system of two quantum dots, the dynamics reveal coherent Rabi oscillations, which one suppressed as time evolves due to the incoherent tunneling to the reservoirs. Both the Rabi frequency and the coherence time are strongly affected by the external source-drain voltage. This coherence is emphasized by the shot-noise signal, which presents a characteristic behavior at the Rabi frequency, being more pronounced when the two levels are in resonance. We also note that the Rabi oscillations are amplified when the interdot hopping is higher than the incoherent tunneling rate. Additionally, we investigated electronic transport of an ensemble of coupled sites that simulates an array of quantum dots or a molecule. An external bias voltage is applied along the structure in order to study the tunneling current, the transmission coefficient, shot noise and Fano factor. While in the linear case the characteristic I-V curve reveals no current rectification, in the disordered configuration a robust rectification is found, thus indicating an operation regime typical of a molecular diode. The negative differential resistance (NDR) is also observed due to the drop of the bias voltage along the structure, that decreases the probability of transmission between the orbital neighbors. We note that when the system becomes disordered the spin correlation tends to increase, with Fano factor reaching values close to 0.4.