Search

In this article we give a review of our recent theoretical studies of the influence of Fe (001) surface (interface) states on spin-polarized electron transport across magnetic tunnel junctions with Fe electrodes. We show that minority-spin surface (interface) states are responsible for at least two effects which are important for spin electronics. First, they can produce a sizable tunneling anisotropic magnetoresistance in magnetic tunnel junctions with a single Fe electrode. The effect is driven by a Rashba shift of the resonant surface band when the magnetization changes direction. This can introduce a new class of spintronic devices, namely, tunneling magnetoresistance junctions with a single ferromagnetic electrode. Second, in Fe/GaAs (001) magnetic tunnel junctions minority-spin interface states produce a strong dependence of the tunneling current spin polarization on applied electrical bias. A dramatic sign reversal within a voltage range of just a few tenths of an eV is predicted. This explains the observed sign reversal of spin polarization in recent experiments of electrical spin injection in Fe/GaAs (001) and related reversal of tunneling magnetoresistance through vertical Fe/GaAs/Fe trilayers.

The mesoscopic transport physics of spin Hall effect and quantized spin Hall effect is briefly reviewed. This paper concentrates on the universal spin Hall conductance fluctuations discovered in both effects. We present various model Hamiltonians corresponding to different physical problems arising recently in condensed matter physics, ranging from two-dimensional electron gas to topological insulators. Green's function formalism within a tight-binding model and the random matrix theory are introduced to study the same electron transport mechanism. The calculated spin Hall conductance results are discussed and some excellent agreement has been found from different approaches. A short summary and our perspectives are provided at the end of paper.

We study shot noise for entangled electrons in a 4-lead beam-splitter with one incoming lead driven by adiabatically rotating magnetic fields. We propose a setup of an adiabatically rotating magnetic field which is appropriate for an electron beam to transport through. Using the scattering matrix approach, we find that shot noise for the singlet and that for the entangled triplet oscillates between bunching and antibunching due to the influence of the Berry phase. It provides us with a new approach for testing the Berry phase in electron transport on the basis of entanglement.

The oscillation of tunnel splitting in Fe8 molecular clusters is obtained as a function of magnetic field applied along the hard axis by means of the instanton method with both effective potential field description of quantum spin system and the semiclassical treatment. The theoretical splittings of the instanton method are compared with the numerical result by diagonalization of the spin Hamilton operator and experimental observations.