Particle-in-cell simulation of ultrafast hot-carrier transport in Fe/Au-heterostructures

TL;DR

This paper presents a spin-dependent particle-in-cell model for ultrafast hot-electron transport in Fe/Au heterostructures, capturing ballistic to diffusive regimes and applied to interpret recent spin-valve experiments.

Contribution

It introduces a versatile, spin-dependent particle-in-cell approach that incorporates lifetimes and transmission coefficients, extendable to multilayer systems and capable of describing various transport regimes.

Findings

Microscopic insight into hot-electron dynamics in Fe/Au structures.

Demagnetization effects occur regardless of magnetic alignment.

Model successfully explains experimental observations in spin-valves.

Abstract

We describe a theoretical approach for spin-polarized hot-electron transport, as it occurs after excitation by ultrafast optical pulses in heterostructures formed by ferromagnetic and normal metals. We formulate a spin-dependent particle-in-cell model that solves the Boltzmann equation for excited electrons. It includes lifetimes and transmission coefficients as parameters, which can be taken from ab-initio calculations or experiment, and can be easily extended to multilayer systems. This approach is capable of describing electron transport in the ballistic, super-diffusive and diffusive regime including secondary-carrier generation. We apply the model to optically excited carriers in Fe/Au bilayers and Fe/Au/Fe spin-valve structures. We gain microscopic insight into the hot-electron transport dynamics probed in recent experiments on spin-valves. We find contributions to the demagnetization dynamics induced in Fe/Au/Fe trilayers regardless of the parallel or antiparallel magnetic alignment of the Fe layers.