Photon-assisted Quantum Transport In Magnetic Semiconductor Heterostructure

In this thesis, the photon-assisted quantum transport properties in magnetic semiconductor heterostructure are investigated by using Floquet theory, the scattering matrix and the effective-mass approximation theory. The sandwich structure formed by magnetic semiconductor/semiconductor/magnetic semiconductor produces a quantum well with Dresselhaus spin-orbit coupling. The magnetizations of two magnetic semiconductor layers are in non-collinear configuration. The external oscillation field in the quantum well region inelastically couples with the transmitted electron. All these factors lead to photon-assisted quantum transport. The main research contents are in following. Firstly, the influence of the magnetization in magnetic semiconductor on the bound state is studied. In the magnetic quantum-well formed by the semiconductor heterostructures, the spin-orbit coupling leads to the level splitting of two bound energy levels corresponding different spin. The height of barrier is changed by the strength of magnetization and the angle between the two magnetized directions, so that the bound state in the quantum well depends on them. The stronger is the magnetization, the more is the influence on the bound state by the angle. Secondly, the modulation of the non-collinear magnetization on Fano resonance is studied. Spin-orbit coupling in the potential region makes the electron spin flip, so two Fano resonance peaks appear even if the spin direction of the incident electron is fixed. The height of each resonance peak is proportional to the probability of corresponding spin flipping. The position of peak depends on the frequency of the external field and the exchange-split energy, and are modulated by the angle. These features can be used to detect the spin flipping. Thirdly, the dependence of the shot noise and the magnetoresistance on non-collinear magnetization is discussed. With the increase of magnetization, when the magnetized angle is adjusted, the peak of magnetoresistance changes into a valley, and there are two peaks at two side of the valley. The magnetoresistance produces the phenomenon of positive and negative alternating. The shot noise at zero temperature changes dramatically with the variation of the angle of magnetization at the low-frequency limit. Shot noise gradually changes from the symmetric shape into asymmetric shape with increasing the exchange splitting energy. For the incidence of the different spin electrons, shot noise has different variation as changing the exchange splitting energy. These results may be helpful to make the magnetic semiconductor heterostructures into the quantum devices.