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Proceedings Paper

Nonlinear sigma-model approach to the coupled spin-charge dynamics in the presence of Rashba spin-orbit coupling (Conference Presentation)

Paper Abstract

Spin-charge coupled dynamics is the subject of fundamental and applied research for its relevance in spintronics. In this context the understanding of the interplay between disorder and spin-orbit coupling (SOC) plays a key role. The nonlinear sigma model for disordered electron systems is a powerful effective field theory for transport phenomena in diffusive conductors and superconductors. At the tree level the nonlinear sigma model is equivalent to the Eilenberger and Usadel equations for the quasiclassical Keldysh Green function. The latter, which were originally developed for superconductors, have been extended in order to include SOC. Here we derive the nonlinear sigma model with Rashba SOC for the disordered two-dimensional electron gas (2DEG). By starting from a functional integral representation of the partition function for disordered fermions in the presence of Rashba SOC, we introduce the Q matrix (in Keldysh and spin space) field to decouple the effective fermion-fermion interaction introduced by the disorder average. After integrating out the fermion degrees of freedom, we get the effective action for the Q field. The saddle-point approximation reproduces the self-consistent Born approximation, in the presence of Rashba SOC. By restricting to the manifold QQ=1, we derive the nonlinear sigma model for diffusive spin and charge density modes. The Rashba SOC appears as a SU(2) gauge field coupled to the Q field. Nonuniform and time-dependent saddle-point solutions for the Q field obey the Usadel equation in the presence of Rashba SOC. Finally, extensions of the theory beyond the 2DEG are briefly discussed.

Paper Details

Date Published: 10 September 2019
Proc. SPIE 11090, Spintronics XII, 110901W (10 September 2019); doi: 10.1117/12.2527690
Show Author Affiliations
Roberto Raimondi, Univ. degli Studi di Roma Tre (Italy)
Alessandro Veneri, Univ. degli Studi di Roma Tre (Italy)

Published in SPIE Proceedings Vol. 11090:
Spintronics XII
Henri-Jean M. Drouhin; Jean-Eric Wegrowe; Manijeh Razeghi, Editor(s)

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