Observation of the crossover between metallic and insulating regimes of the spin Hall effect

Hiroyuki Moriya,Satoshi Haku,Akira Musha,Kazuya Ando

doi:10.1038/s42005-021-00791-1

Abstract

The physics of the anomalous and spin Hall effects is one of the most intriguing aspects of condensed matter physics. An important finding from a large collection of experimental and theoretical results is the universal scaling of the anomalous or spin Hall conductivity with the electric conductivity. This scaling has been successfully described by the intrinsic Berry curvature and extrinsic scattering mechanisms for metallic systems, revealing the topological nature of these effects. In contrast, the underlying physics in the opposite limit, the disordered insulating regime, is still unclear. In particular, it remains a major challenge, both experimentally and theoretically, to explore the spin Hall effect in the insulating regime. Here, we report the observation of the crossover between the metallic and insulating regimes of the spin Hall effect. The result demonstrates a direct correspondence between the spin and anomalous Hall effects, which will advance the fundamental understanding of spin transport.

Highlights

The physics of the anomalous and spin Hall effects is one of the most intriguing aspects of condensed matter physics
Between the anomalous Hall conductivity σxy and the longitudinal conductivity σxx; (i) the superclean regime, where σxy ∝ σxx due to the dominant contribution from the skew-scattering, (ii) the moderately dirty regime, where the intrinsic mechanism is dominant, and σxy is roughly insensitive to σxx, and (iii) the dirty regime with the scaling exponent γ generically larger than unity
The interfacial spin-orbit torques originating at the TiN/PtOx interface play a minor role in the Ni81Fe19/TiN/PtOx film because interfacial spin-orbit coupling (SOC) effects are notable only when PtOx is directly contacted with Ni81Fe1918. These results indicate that the sizable symmetric voltage VDC observed for the Ni81Fe19/TiN/PtOx films originates from the DL

Summary

Introduction

The physics of the anomalous and spin Hall effects is one of the most intriguing aspects of condensed matter physics. An important finding from a large collection of experimental and theoretical results is the universal scaling of the anomalous or spin Hall conductivity with the electric conductivity. This scaling has been successfully described by the intrinsic Berry curvature and extrinsic scattering mechanisms for metallic systems, revealing the topological nature of these effects. The SHE in metallic systems arises from intrinsic and extrinsic contributions, the mechanisms that are responsible for the anomalous Hall effect (AHE) in ferromagnets[2]. The discovery of the crossover of the AHE has provided important information for the fundamental understanding of the physics of spin transport

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