Out-of-Plane Nonlinear Orbital Hall Torque

TL;DR

This paper introduces a novel approach to generate out-of-plane orbital torques using the nonlinear orbital Hall effect, significantly advancing orbitronic device capabilities by leveraging topological band features.

Contribution

It proposes a new method to produce out-of-plane orbital torques via nonlinear orbital Hall effect, amplified by topological degeneracies, validated through theory and first-principles calculations.

Findings

Nonlinear orbital Hall effect can generate out-of-plane orbital torques.

Topological degeneracies dramatically amplify the nonlinear orbital response.

Orbital torques from this mechanism surpass previous linear mechanisms.

Abstract

Despite recent advances in orbitronics, generating out-of-plane orbital torques essential for field-free deterministic switching of perpendicular magnetization remains a key challenge. Here, we propose a strategy to produce such unconventional torques across broad classes of materials, by leveraging the nonlinear orbital Hall effect. We demonstrate that this nonlinear orbital response is dramatically amplified by topological band degeneracies, where it overwhelmingly dominates the spin response even in systems with strong spin-orbit coupling. These features are confirmed via a quantitative investigation of representative topological metals RhSi, YPtBi, and PbTaSe$_2$, by combining our theory with first-principles calculations. The resulting orbital torques substantially surpass those from linear mechanisms reported thus far. These findings propel the research of orbital transport into the nonlinear regime, broaden the scope of orbital source materials, and establish a new pathway towards high-performance orbitronic devices.