Numerical study of dephasing in disordered electron systems

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In this project, we have studied numerically dephasing and related topics in quantum transport in disordered electron systems where complex quantum interference plays an important role. The interference is especially important in low dimensional systems such as the 2 dimensional electron system (2DES). The breakdown of the interference due to the coupling to external degrees of freedom such as a heat bath is the origin of dephasing. Attaching extra lead(s) coupled to reservoir(s) is a way to take into account the dephasing in numerical calculations. In this project, therefore, we have studied the following :1) Study of electron transport in the 3 terminal geometry : to take into account the dephasing, study of systems with more than two terminals is needed. We have developed a program to study this issue, and have calculated the transport coefficients. As a byproduct, we have analyzed the generation of spin polarized current in the presence of spin-orbit interaction. (Papers 2 and 4.)2 … More ) Study of the role of spin in quantum transport phenomena : the role of the spin degree of freedom in quantum transport has been studied. Of particular interest is the system with strong spin-orbit scattering in low dimensional systems. We have simulated conductance fluctuations (paper 10), the Anderson transition in 2DES (papers 8 and 15) and the Anderson transition below 2 dimensions (paper 1). Dephasing in the presence of spin-orbit scattering has been studied in the 2DES by assuming a time-dependent potential (paper 14).3) Study of random phase model : to investigate the importance of phase in quantum transport, we have studied the random phase model (papers 6 and 11).4) Study of quantum network model : the network model that is a simplified model to study the quantum transport phenomena has been studied (paper 5). Since the model is simple, we are able to attach many leads to a sample.5) Study of edge states in the quantum Hall effect : the quantum Hall edge states are know to have extraordinary long dephasing time. We have studied these states in the presence of disorder in detail (papers 3 and 7). Less