Femtosecond photocurrents by the Dresselhaus bulk spin-galvanic effect in an inversion-asymmetric ferromagnet

TL;DR

This paper demonstrates ultrafast photocurrents in a ferromagnetic Heusler compound driven by the Dresselhaus spin-galvanic effect, revealing a new mechanism for spin-charge conversion with potential spintronic applications.

Contribution

It reports the observation of the Dresselhaus bulk spin-galvanic effect in a ferromagnetic metal, expanding the understanding of ultrafast spin-charge conversion phenomena.

Findings

Photocurrents exhibit Rashba- and Dresselhaus-type symmetry.

Dresselhaus photocurrent relaxes within 10 fs due to electron cooling.

The effect offers a new route for spintronic terahertz emitters.

Abstract

We study ultrafast photocurrents in thin films of a model ferromagnetic metal with broken bulk inversion symmetry, the half-metallic Heusler compound NiMnSb, following excitation with an optical pump pulse with photon energy 1.55 eV. Remarkably, in terms of the direction of the sample magnetization M, all photocurrents are found to be a superposition of a component with Rashba- and Dresselhaus-type symmetry. We explain the Dresselhaus bulk photocurrent as follows: Pump-induced electron heating induces an excess of spin {\mu}_s||M, which transfers spin angular momentum into states with Dresselhaus-type spin-momentum locking. The resulting charge current relaxes on a time scale of 10 fs by momentum relaxation and, thus, follows {\mu}_s quasi-instantaneously. The relaxation of {\mu}_s is governed by the cooling of the electrons and not by the significantly slower spin-lattice relaxation of half-metals. Our findings add the Dresselhaus spin-galvanic effect (SGE) to the set of ultrafast spin-charge-conversion phenomena. They indicate a route to more efficient spintronic terahertz emitters and detectors based on the volume scaling of the bulk SGE.