No abstract

The electronic structure, phonon dispersions, and electron-phonon (EP) coupling in Fe2Se2/SrTiO3 (FeSe/STO) thinnest films are studied based on the first-principles calculations. It is found that the FeSe/STO interface with lattice strain leads to a change of band structures and a significant enhancement of the EP coupling, the latter being close related to interface-induced ferroelectric phonons coupled to electrons on the FeSe monolayer. In the FeSe/STO system, Tc of phonon-induced superconductivity is estimated to be much greater than that in the bulk FeSe, but still well below the experimental value of an FeSe monolayer on the STO substrate, indicating that the electron-phonon mechanism alone cannot explain its high Tc.

A one-dimensional electron model with parameters modulated adiabatically in closed cycles is proposed which can continuously pump spin to leads. By defining the spin-polarized Wannier functions, we reveal that the spin pumping is protected by the spin Chern numbers, so that it is stable to perturbations violating the time-reversal symmetry and spin conservation. Our work demonstrates the principle for realizing robust topological spin pumps independent of the time-reversal symmetry. A possible way to directly observe the bulk topological invariants is also suggested.

No abstract

A macroscopic theory of giant magnetoresistance in granular magnetic materials is developed to improve on that of Rubinstein ͓Phys. Rev. B 50, 3830 ͑1994͔͒. By using a self-consistent method and introducing a useful parametrization, we show the magnetotransport in granular systems to be between those for currents in the plane of layers and currents perpendicular to the plane of the layers in multilayers. The theoretical result in the local limit is found to be in agreement with the observed singular dependence of the giant magnetoresistance on annealing temperature.