چكيده به لاتين
In this thesis spin polarization and spin current in quantum ring arrays caused by two-dimensional electron gas were studied. First, spin related conductance and polarization via an open ballistic quantum nanoring connected to one input lead and two output ones are studied by considering the Rashba effect based on the transfer matrix method. Our probes show that controlling on Rashba strength leads to 100 percent spin polarization while we have high efficiency for the system. In addition, it is possible to design the position of input and output leads in such a way as to optimize the system to work as a spin filtering or spin switching nano device. Also, this apparatus can work as a Stern-Gerlach tool which can be used in some important practical nano-industrial applications. By controlling on Rashba strength in a special design of two output lead positions, it is possible to divide the input charge current into any output ones while the partial output charge current has substantial value in one of two output leads and it is reduced in the other one simultaneously. By controlling on Rashba strength in a special design of output lead positions, the spin conductance can attain a considerable value in one output lead despite an insignificant value in the other one simultaneously. Based on the scattering matrix method the coupling effects on the electronic spin dependent transport properties through a one-dimensional quantum nano ring connected to two leads, in the presence of Rashba spin-orbit interaction (RSOI) with strength α and the effect of Aharonov-Bohm is studied. By tuning Rashba strength via external gate and Aharonov-Bohm intensity, it is possible to obtain conditions which the system acts as a perfect spin-filtering device with high efficiency and a full range spin polarizer. The perfect spin filtering and spin polarization with high- efficiency can take place in narrow ranges of incident electron energies for weak coupling, while for strong one it can occur in a wide range of energies which have appropriate application in nano science industry. The effective spin polarization and spin filtering of a linear chain of N one-dimensional nanorings in the presence of the Rashba and Aharonov–Bohm effects are studied by considering three different lead–ring coupling regimes. Utilizing the transfer-matrix method, the optimal number of rings for maximizing the system efficiency is determined in the weak, medium, and strong lead–ring coupling regimes. The strong coupling regime is proposed for the design of spintronic devices as it exhibits the highest system efficiency. Furthermore, by tuning the Rashba strengths in the rings alternately, perfect spin filtering and full-range spin polarization with high efficiency can be obtained in narrow ranges of the incident electron wavenumber. Moreover, controlling the Rashba strength leads to the design of energy-filtering devices with a desired spin polarization, which could play a dominant role in spintronic technology. The effects of lead positions and lead-ring coupling regimes are investigated on spin-related transport through a two-dimensional network of quantum nanorings (TDNQRs) considering Rashba spin-orbit interaction (RSOI) and magnetic flux. A matrix representation for the transmission and reflection coefficients through a single ring connected to the arbitrary number of leads has been introduced. As a specific example of TDNQRs, the conductance, spin polarization, and system efficiency are obtained via a triangular network of quantum rings (TNQRs). TNQRs behaves completely opaque or transparent versus RSOI strength and wave vector (k) of the incident electron. The periodicity of these functions along the k axis depends on the lead positions and is independent of lead- ring coupling. Also, the symmetric geometry and strong lead-ring coupling regime significantly improve the performance of the system as a multi-purpose spintronic device (i.e., a perfect spin filter, spin-splitter, spin switching, Stern-Gerlach device, and an electronic switching device) .
