SPIN AND PSEUDOSPIN TRANSFER

Abstract

Electrons in a Fermi liquid can be regarded as non-interacting particles (quasiparticles) in an effective potential that is a consequence of interactions between electrons. In many-body theory the effective potential is known as the electronic self-energy. When the electronic system has a broken symmetry, the effective potential can have different symmetries than the potential term that appears in the single particle Hamiltonian. For example, the effective potential of a superconductor includes terms that change the electron particle number and the effective potential of a ferromagnet includes terms that change the electron spin. When the electron system is not in equilibrium, the effective potential is altered. I will present a view of spin-transfer phenomena in ferromagnetic metals in which current-induced spin torques arise from changes in the ferromagnet's spin-dependent effective potential when the quasiparticle system is held out of equilibrium by applying a bias potential. In this view spin-transfer is an example of a more general set of phenomena and is not fundamentally associated with an approximate conservation law, for example the approximate conservation of total spin angular momentum. I will illustrate this point of view by discussing other examples of spin-transfer like phenomena, including transport anomalies that have been observed in bilayer quantum Hall systems, current-driven magnetization changes in antiferromagnetic metals, and current-drive bond-weakening in molecular electronics. Note from Publisher: This article contains the abstract only.