Ultrafast transport of laser-excited spin polarized carriers in Au/Fe/MgO(001)

TL;DR

This study demonstrates a time-resolved method to observe ultrafast spin-polarized hot carrier transport in Au/Fe/MgO(001), revealing superdiffusive propagation and spin-dependent lifetimes of carriers excited by femtosecond laser pulses.

Contribution

It introduces a novel time domain approach to directly measure ultrafast spin-polarized carrier dynamics in epitaxial heterostructures.

Findings

Spin-polarized hot carriers propagate superdiffusively at different velocities.

Two distinct spin current contributions result in a ~100 fs spin current pulse.

Spin-dependent lifetimes of hot carriers are observed in Au.

Abstract

A time domain approach to probe hot carrier-induced spin dynamics is demonstrated. The experiments are performed in epitaxial Au/Fe/MgO(001), where spin-polarized hot carriers are excited in the Fe layer by 35 fs laser pulses. They propagate to the Au surface where the transient spin polarization is detected by magneto-induced second harmonic generation. Different energies of majority and minority hot carriers excited in the exchange-split Fe band structure lead to their spindependent lifetimes in Au. Accordingly, two spin-polarized current contributions which propagate superdiffusively at different velocities result in a spin current pulse of about 100 fs duration.