Sub-picosecond temporal resolution of anomalous Hall currents in GaAs

Christian B Schmidt,Shekhar Priyadarshi,Mark Bieler

doi:10.1038/s41598-017-11603-4

Abstract

The anomalous Hall (AH) and spin Hall effects are important tools for the generation, control, and detection of spin and spin-polarized currents in solids and, thus, hold promises for future spintronic applications. Despite tremendous work on these effects, their ultrafast dynamic response is still not well explored. Here, we induce ultrafast AH currents in a magnetically-biased semiconductor by optical femtosecond excitation at room temperature. The currents’ dynamics are studied by detecting the simultaneously emitted THz radiation. We show that the temporal shape of the AH currents can be extracted by comparing its THz radiation to the THz radiation emitted from optically induced currents whose temporal shape is well known. We observe a complex temporal shape of the AH currents suggesting that different microscopic origins contribute to the current dynamics. This is further confirmed by photon energy dependent measurements revealing a current inversion at low optical excitation intensities. Our work is a first step towards full time resolution of AH and spin Hall currents and helps to better understand the underlying microscopic origins, being a prerequisite for ultrafast spintronic applications using such currents.

Highlights

Employing the spin degree of freedom for information processing enables promising new applications[1, 2]
Currents whose temporal shape is well known. Taking advantage of this approach we demonstrate that the anomalous Hall (AH) currents possess a complex temporal shape, which depends on excitation intensity and photon energy
The geometry is similar to the one used by Bakun et al.[12], just that the generation and detection of the AH current are accomplished in a time-resolved manner

Summary

Introduction

Employing the spin degree of freedom for information processing enables promising new applications[1, 2]. This can be realized using the spin Hall[3,4,5] and inverse spin Hall[6, 7] effects, converting charge currents into spin currents and vice versa, respectively Both effects result from the microscopic mechanisms being responsible for the anomalous Hall (AH) effect, which denotes a deflection of carriers into an apparently “anomalous” direction. Time resolved measurements of the anomalous velocity[16] might be a possibility to distinguish between intrinsic and extrinsic effects and to gain new insight into the underlying microscopic origins, calling for additional time-resolved studies. A spin component perpendicular to the velocity is required for AH current generation In this geometry the Berry curvature and the scattering centers interact with the spin to modify the direction of motion of the carriers and lead to AH currents

Methods

Results

Conclusion