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, topological insulator (TI) surfaces and nanowires (NWs) and topological semimetals.
The first principles methods typically involve the density functional theory calculations carried out with state-of-the-art codes such as: Wien2K, VASP, Siesta, Transiesta, SMEAGOL and NRLMOL. The implantation and running of these programs for the systems considered in the application require the use of extensive supercomputer facilities.
Specific goals for the next year (Feb 2018 - Jan 2019) are:
1) to study quantum the anomalous Hall effect in magnetically doped binary-chalcogenide TIs using first-principles methods.
2) to model spin-dependent transport in (Ga,Mn)As and binary-chalcogenide topological-insulator nanowires.
3) to study spin-dependent transport in magnetic material/topological insulator heterostructures, magnetic material/Weyl semimetal heterostructures and magnetic material/Dirac semimetal heterostructure using first-principles non equilibrium Green’s function method based on the Smeagol code. In particular, we will investigate how the magnetization at the interface can be controlled through the spin-orbit torque (SOT) and spin-transfer torque (STT).
These first three projects will provide crucial theoretical support to a parallel experimental activity being developed at LNU. and based on the use of molecular bean epitaxy (MBE) techniques. This collaboration is partly supported by two granted VR grants (one with C.M. Canali as PI running for the period 2015-2018; the second recently approved for the period 2018-2021, with J. Sadowski, responsible for the MBE, as PI, and C.M. Canali as co-applicant.)
Other ongoing projects that will continue in 2018-2019:
4) 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
5) 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
6) to investigate the formation and stability of magnetic nanoclusters on the surfaces of GaAs semiconductor using first principles methods.
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 further develop theoretical modeling of scanning tunneling microscopy based in first-principles methods, and apply these modelling to the physical systems involving metal and semiconductor nanostructures
9) to study electron and heat transport in nano-junctions