Unconventional orbital currents and torques due to ferro-rotational orbital textures

TL;DR

This paper demonstrates that ferro-rotational order can generate unconventional orbital currents electrically, offering a new pathway for orbitronics beyond the traditional orbital Hall effect, with potential for magnetic device manipulation.

Contribution

It introduces a novel mechanism for orbital current generation via ferro-rotational order, supported by models and first-principles calculations, expanding the scope of orbitronics research.

Findings

Ferro-rotational order enables electrical generation of unconventional orbital currents.

These currents are linked to an electric hexadecapole moment.

Surface orbital accumulation and orbital torque can be achieved in bilayer structures.

Abstract

Orbital angular momentum transport has emerged as a promising route for manipulating magnetic devices, yet its generation has largely relied on the conventional orbital Hall effect. Here, we show that ferro-rotational order enables the electrical generation of unconventional orbital currents. These orbital currents represent the orbital counterparts of spin currents due to ferromagnetic order, but arise from rotation-induced symmetry breaking rather than time-reversal symmetry breaking or spin-orbit coupling. Using tight-binding models, we identify the underlying intrinsic, nonrelativistic mechanism categorized as an electric hexadecapole moment and corroborate our findings with first-principles calculations for the ferro-rotational material TiAu$_4$. We further show that these rotation-induced orbital currents lead to surface orbital accumulation and unconventional orbital torque in a ferro-rotational/ferromagnetic metallic bilayer, allowing deterministic field-free switching. Our findings unveil a novel pathway for generating orbital currents beyond the conventional orbital Hall effect, broadening the landscape of orbitronics research to include novel ferroic materials and higher-order electric multipoles.