Observation of gigantic spin conversion anisotropy in bismuth

TL;DR

This study demonstrates a gigantic spin conversion anisotropy in bismuth caused by its highly anisotropic g-factor, revealing new insights into spin physics influenced by spin-orbit interaction.

Contribution

It provides the first experimental evidence linking large g-factor anisotropy to significant spin conversion efficiency in bismuth, combining experimental and theoretical approaches.

Findings

Spin-torque ferromagnetic resonance shows 17% spin conversion efficiency in Bi(110).

Harmonic Hall measurements confirm large spin conversion efficiency.

First observation of gigantic spin conversion anisotropy due to g-factor anisotropy.

Abstract

Whilst the g-factor can be anisotropic due to the spin-orbit interaction (SOI), its existence in solids cannot be simply asserted from a band structure, which hinders progress on studies from such the viewpoints. The g-factor in bismuth (Bi) is largely anisotropic; especially for holes at T-point, the g-factor perpendicular to the trigonal axis is negligibly small (< 0.112), whereas the g-factor along the trigonal axis is very large (62.7). We clarified in this work that the large g- factor anisotropy gives rise to the gigantic spin conversion anisotropy in Bi from experimental and theoretical approaches. Spin-torque ferromagnetic resonance was applied to estimate the spin conversion efficiency in rhombohedral (110) Bi to be 17%, which is unlike the negligibly small efficiency in Bi(111). Harmonic Hall measurements supports the large spin conversion efficiency in Bi(110). This is the first observation of gigantic spin conversion anisotropy as the clear manifestation of the g-factor anisotropy. Beyond the emblematic case of Bi, our study unveiled the significance of the g-factor anisotropy in condensed-matter physics and can pave a pathway toward establishing novel spin physics under g-factor control.