A non-equilibrium quantum transport framework for spintronic devices with dynamical correlations

TL;DR

This paper introduces a new quantum transport framework combining DFT, NEGF, and DMFT to model spintronic devices with dynamical correlations under non-equilibrium conditions, capturing complex electron interactions.

Contribution

The framework integrates dynamical mean-field theory with existing methods to accurately model non-equilibrium spintronic transport beyond single-particle approximations.

Findings

Correlations induce a Fermi-liquid to non-Fermi-liquid transition in Co under bias.

Fe/MgO/Fe junctions show weaker correlation effects, remaining near equilibrium.

Inelastic scattering influences transport properties and device response to bias.

Abstract

Two-terminal spintronic devices remain challenging to model under realistic operating conditions, where the interplay of complex electronic structures, correlation effects and bias-driven non-equilibrium dynamics may significantly impact charge and spin transport. Existing {\it ab initio} methods either capture bias-dependent transport but neglect dynamical correlations or include correlations but are restricted to equilibrium or linear-response regimes. To overcome these limitations, we present a framework for steady-state quantum transport, combining density functional theory (DFT), the non-equilibrium Greens' function (NEGF) method, and dynamical mean-field theory (DMFT). The framework is then applied to Cu/Co/vacuum/Cu and an Fe/MgO/Fe tunnel junction. In Co, correlations drive a transition from Fermi-liquid to non-Fermi-liquid behavior under finite bias, due to scattering of electrons with electron-hole pairs. In contrast, in the Fe/MgO/Fe junction, correlation effects are weaker: Fe remains close to equilibrium even at large biases. Nevertheless, inelastic scattering can still induce partly incoherent transport that modifies the device's response to the external bias. Overall, our framework provides a route to model spintronic devices beyond single-particle descriptions, while also suggesting new interpretations of experiments.