MAGNETISM AND NANOSPINTRONICS IN SEMICONDUCTOR NANOSTRUCTURES, TOPOLOGICAL INSULATORS AND MOLECULAR MAGNETS
The objective of this proposal is to study spin-dependent transport and tunneling spectroscopy in novel magnetic nanostructures. Focus is on nanomagnets whose structure is either controlled by chemical synthesis such as single molecule magnets, or engineered by manipulating individual magnetic atoms inside advanced quantum materials, such as semiconductor and topological insulator (TI) surfaces and nanowires (NWs). Specific goals are: 1) to develop first-principle approaches of quantum transport through a single molecular magnet (SMM) attached to metallic and possibly magnetic leads; we will also investigate theoretically mechanisms that allow efficient manipulation of the spin states of a SMM by means of an external electric field 2) to develop further and refine quantum models of transition-metal clusters incorporated on a semiconductor surface or in a semiconductor nanowire, in order to elucidate at the atomic scale the mechanisms of the hole-mediated exchange interaction between magnetic dopants in ferromagnetic semiconductors and in semiconductor nanostructures; theoretical approaches to quantum tunneling transport in these structures will also be investigated 3) to study quantum anomalous Hall effect in magnetically doped binary-chalcogenide TIs using first-principles methods. 4) to investigate the formation and stability of magnetic nanoclusters on the surfaces of GaAs semiconductor using first principles methods. 5) to continue our experimental studies of spin-dependent transport through a gated semiconductor NW, attached to metallic leads, with emphasis on spin-injection from a ferromagnet into the NW, spin detection and manipulation; we will also investigate the effect on transport caused by magnetic impurities implanted in the NWs; for this case, optical measurements will complement transport studies; theoretical modeling of the system (see previous section), as well as of the transport and optical properties will support the experiments 6) to study electron and heat transport in nano-junctions 7) to study theoretically the quantum spin dynamics and spin relaxation of STM-engineered magnetic clusters probed experimentally by inelastic electron tunneling spectroscopy (IETS); an impulsive approximation, suitable to describe the strong coupling between tunneling electrons and local magnetic excitations, will be implemented within a first-principle theory of IETS, based on the Transiesta code 8) to model spin-dependent transport in (Ga,Mn)As and binary-chalcogenide topological-insulator nanowires.