Density-Functional Approximation for the Spin Dependent Quantum Transport in Magnetic Nanostructures

摘要

In quasi-classical theoretical framework, the transport of electrons and holes in semiconductor devices is treated with the Boltzmann transport equation (BTE) or quantum-mechanical energy band theory - viz., the effective mass approximation and the random phase approximation. On the other hand, in the mesoscopic, nanoelectronic devices, for three- and lower- dimensional structures with nanometer scaling, the wave properties, spin, charge and the interactions between spin and charge of electrons are fully utilized such as in artificial mini-Brillouin zones, quantum size effects, Coulomb blockade of single-electron tunneling and spin-polarized giant magnetoresistance (GMR) tunneling. The complexity associated with the classical quantum-mechanical formalism in the study of transport in magnetic nanostructures can be avoided by applying the so-called, Hohenberg-Kohn's density functional theory. Because of the limitations of quasi-classical theory, it is more appropriate to treat the magneto-transport problem in nanostructures by using quantum many-body theory. The starting point of the quantum trans-port theory is to take an external field as a perturbation for the many-particle system in equilibrium. This leads to a linear response and gives corresponding transport coefficients. One useful application of the Green's function techniques in quantum magneto-transport is to convert a homogeneous differential equation into an integral equation, viz., as in the time-dependent Schrodinger equation. We have applied it to scattering of nanostructural defects (impurities) in the electron gas (metal) as many-body effect's model and derived an expression for its residual resistivity. Calculations of magnetic impurities in noble-metal hosts are in good agreement with the previously published results.