Ab-Initio Studies of Spin-Orbit and Electron-Phonon Effects in Metals

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

TECHNICAL SUMMARY: This award supports theoretical and computational research and education in the area of the electronic structure of metals, with particular emphasis on properties mediated by the spin-orbit and electron-phonon interactions. These interactions induce subtle modifications in the electronic structure and accurately calculating the consequences represents a significant challenge. A major focus of the proposed work will be to further develop efficient and accurate algorithms for treating spin-orbit effects which can effectively address the need to sample the entire Brillouin zone in metallic systems. The method developed here capitalizes on a means for representing the bulk electronic structure in terms of partially occupied spinor Wannier functions and will be applied to two types of problems: First, in regard to spin relaxation in nonmagnetic metals, a previously proposed mechanism of spin relaxation, resulting from the combination of spin-orbit and electron-phonon coupling, will be investigated from first-principles. Initial studies will focus on trivalent metals such as aluminum, which are particularly challenging due to the occurrence of spin-orbit "hot spots" on the Fermi surface. Second, spin-orbit effects in ferromagnets in which time-reversal symmetry may be spontaneously broken will be investigated computationally from first principles. The specific properties of study are the intrinsic dc anomalous Hall effect, magneto-optical effects such as magnetic circular dichroism, and orbital magnetization. Applications will be made first to itinerant ferromagnets such as iron, nickel, and cobalt. In parallel with the ab-initio studies, theoretical work will be carried out to reveal the interconnections between the various spin-orbit effects in ferromagnets. The second major focus of research is to extend the Wannier-interpolation algorithms to calculate the electron-phonon coupling matrix elements, by representing the physics in terms of both localized electronic and vibrational lattice Wannier functions. The resulting technique will be applied to both spin-relaxation mechanism and superconductivity in boron-doped diamond. This project is expected to lead to fundamental theoretical and algorithmic advances aiming to accurately and reliably calculating spin-orbit and electron-phonon physics in metals. It will provide an improved understanding of the mechanisms by which the spin-orbit interaction gives rise to the dc anomalous Hall conductivity in ferromagnets. It will extend to finite frequency the algorithms developed for the anomalous Hall conductivity, and allow for the exploration of magneto-optical effects. It will uncover rather subtle sum rules which connect these dynamical properties to the static orbital magnetization. NON-TECHNICAL SUMMARY: This award supports theoretical and computational research and education that aims to develop and apply methods that will enable computers to calculate magnetic properties of and phenomena in materials with a focus on understanding how electrons, the tiny units of charge and magnetism in a material, move through materials when driven by electric and magnetic fields. The discovery of new magnetic phenomena as well as learning how to control known magnetic phenomena continues to lead to new technologies and conspicuously to advances in information technology. These technologies include spintronics, photomagnetic devices, magnetic memory and storage devices and magnetoelastic materials. Computer assisted design of magnetic materials and devices still requires theoretical and methodological advances. This research deals aims to develop a method at the level of atoms and electrons for accurately calculating magnetic properties of materials. Such methods will enable scientists and engineers to open new frontiers and technologies.