Study On Electronic Transport Properties In Ferromagnetic/nonferromagnetic Heterojunctionand In Quantum Ring With Multiple Arms

In this paper we theoretically investigate the electronic transport phenomena in the ferromagnetic/nonferromagnetic/ferromagnetic heterojunction and the quantum ring with multiple arms structure, which possess great potential in future applications. We expect to provide theoretical foundation for the development of novel quantum devices with our work. The main results obtained in this paper are listed below: (1) The quantum size, quantum coherence, and Rashba spin-orbit coupling are considered simultaneously in this paper. Using the model of Rashba spin-orbit coupling, we investigate the transmission coefficient in the ferromagnetic/ nonferromagnetic/ferromagnetic heterojunction. Our results demonstrate that the transmission coefficient shows typical resonant transmission properties. As the length of the semiconductor increases, the transmission coefficient oscillates more rapidly, the peaks become sharper, and the intervals between adjacent peaks are narrowed. (2) Based on the group velocity concept, we investigated the traversal time in the ferromagnetic/nonferromagnetic/ferromagnetic heterojunction in the presence of Rashba spin-orbit coupling. Our results indicate that the Rashba spin-orbit coupling obviously decreases the traversal time. The results also indicate that the traversal is not prolonged linearly as the length of the semiconductor increases but shows step-like behavior. (3) We proposed a new quantum ring structure with multiple arms and developed the expression of the transmission coefficient. The results show that the amount of peaks in one period is equal to the amount of the wave functions in the multiarm rings. The results also show that the structure of has more larger conductance than that of the case except near the singular point, and the results further show the ratio of is larger than .(4) We developed an equivalent method to investigate the persistent current in the ring with multiple arms and then applied to the triple-arm open AB rings. The numerical results show that the persistent currents are different in each arm, which is quite different than the case of the single or coupled ring. The studies further show that the difference of the persistent current in the considered system with broken time-reversal symmetry is not caused by the magnetic flux but by the different states of electron in each arm.