Study of Quantum Transport in Low Dimensional Electrons in Superperiodic Structures

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The band theory which constitutes the basis of solid state physics, is essentially a description of the behavior of electrons in periodic potential. In this research project, we have investigated transport phenomena that originate from superperiodic structures. The materials investigated are natural and artificial layred materials including organic conductors, graphite interacalation compounds, semiconductor superlattices and metallic multilayrs. We also studied two-dimensional electron system at the interface of semiconductors with microstructured gate electrode. The superconducting magnet system purchased with this grant has been also effectively used in studies of diluted magnetic semiconductors.The followings are the main research acomplishments :By fabricating GaAs/AlGaAs heterostructures with microstructured ferromagnetic gate electrode on the surface, we have succeeded in applying spatially modulated magnatic field to two-dimensional electron gas. We predicted earlier that in a unidirectional modulation of magnetic field. the magnetoresistance shows commensurability oscillation effect. which we have experimentally verified in this research term.Angular-dependent magnetoresistance oscillation (ADMRO) is a phenomenon discovered in (BEDT-TTF)-based organic conductors. We have shown theoretically that it is a generic property of quasi-two-dimensional Fermi surface, and experimentally verified it by observing the ADMRO in graphite intercalation compounds and also in GaAs/AlGaAs superlattice.(BEDT-TTF)2KHg(SCN)4 exhibits a different type of ADMRO.We have clarified that it originates from the commensurability of open orbits on a quasi-one dimensional Fermi surface with the underlying unit cell by mapping of the resistivity dips from two-axis rotation measurement and by model calculations.