Emergent spin Hall conductivity in Tantalum-Rhenium alloys

TL;DR

This study explores how the spin Hall conductivity in Ta-Re alloys varies with composition, revealing a significant enhancement at specific stoichiometries due to Fermi level tuning, supported by experimental and theoretical analysis.

Contribution

It demonstrates the emergence of enhanced spin Hall conductivity in Ta-Re alloys at certain compositions, combining experimental THz emission measurements with theoretical band structure modeling.

Findings

Maximum SHC at ~60% Ta composition

Fermi level tuning explains SHC variation

Experimental validation via THz emission

Abstract

We investigate the spin Hall conductivity (SHC) of a composition series of a Ta-Re bcc solid solution. At approximately 60 at.% Ta the Ta-Re alloy features an SHC similar to bcc-W, while both endpoints of the compositional series have rather moderate SHC. The intermediate stoichiometries exhibit a substantial enhancement due to Fermi level tuning through the same band structure feature which gives bcc-W and $\beta$-W its large SHC. We provide experimental evidence for the enhancement of the SHC in the alloy via THz emission upon ultrafast laser excitation of Ta-Re/CoFeB bilayers. We demonstrate that a rigid band model derived from bcc-W and Fermi level tuning describes the experimental data with a similar accuracy as coherent potential approximation alloy calculations of the SHC.