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Current Induced Order Parameter Dynamics: Microscopic Theory Applied to Co/Cu/Co spin valves

P. M. Haney·D. Waldron·R. A. Duine·A. S. Nunez·H. Guo·A. H. MacDonald
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Abstract

Transport currents can alter alter order parameter dynamics and change steady states in superconductors, in ferromagnets, and in hybrid systems. In this article we present a scheme for fully microscopic evaluation of order parameter dynamics that is intended for application to nanoscale systems. The approach relies on time-dependent mean-field-theory, on an adiabatic approximation, and on the use of non-equilibrium Greens function (NEGF) theory to calculate the influence of a bias voltage across a system on its steady-state density matrix. We apply this scheme to examine the spin-transfer torques which drive magnetization dynamics in Co/Cu/Co spin-valve structures. Our microscopic torques are peaked near Co/Cu interfaces, in agreement with most previous pictures, but suprisingly act mainly on Co transition metal $d$-orbitals rather than on $s$-orbitals as generally supposed.

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P. M. Haney, D. Waldron, R. A. Duine, A. S. Nunez, H. Guo, A. H. MacDonald. 2006-11-20. Current Induced Order Parameter Dynamics: Microscopic Theory Applied to Co/Cu/Co spin valves. https://doi.org/10.1103/physrevb.76.024404

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