ELECTRONIC STATES AND MAGNETOTRANSPORT IN QUANTUM WAVE-GUIDES WITH NONUNIFORM MAGNETIC-FIELDS

The electronic states and magnetotransport properties of quantum waveg uides (QW's) in the presence of nonuniform magnetic fields perpendicul ar to the QW plane are investigated theoretically. It is found that th e magnetoconductance of those structures as a function of Fermi energy exhibits stepwise variation or square-wave-like oscillations, dependi ng on the specific distributions (both in magnitude and direction) of nonuniform magnetic fields in QW's. We have investigated the dual magn etic strip structures and three magnetic strip structures. The charact er of the magnetotransport is closely related to the effective magneti c potential and the energy-dispersion spectrum of electron in the stru ctures. It is found that dispersion relations seem to be combined by d ifferent sets of dispersion curves that belong to different individual magnetic subwaveguides. The magnetic effective potential leads to the coupling of states and the substantial distortion of the original dis persion curves at the interfaces in which the abrupt change of magneti c fields appears. Magnetic scattering states are created. Only in some three magnetic strip structures, these scattering states produce the dispersion relations with oscillation structures superimposed on the b ulk Landau levels. It is the oscillatory behavior in dispersions that leads to the occurrence of square-wave-like modulations in conductance .