Engineering of Orbital Hybridization: An Exotic Strategy to Manipulate Orbital Current

TL;DR

This paper demonstrates that engineering copper oxidation states in CuO$_x$ heterostructures significantly enhances orbital current and spin-orbit torque efficiency, offering a new strategy for spin-orbitronics without relying on strong spin-orbit coupling.

Contribution

It introduces an orbital hybridization engineering approach in CuO$_x$ heterostructures to boost orbital currents and SOT efficiency, independent of traditional spin-orbit coupling mechanisms.

Findings

Orbital hybridization is enhanced by increasing copper oxidation state.

Torque efficiency is nearly ten times larger than in conventional heavy metals.

Redox reactions can switch the torque efficiency between high and low states.

Abstract

Current-induced spin-orbit torque (SOT) plays a crucial role in the next-generation spin-orbitronics. Enhancing its efficiency is both fundamentally and practically interesting and remains a challenge to date. Recently, orbital counterparts of spin effects that do not rely on the spin-orbit coupling (SOC) have been found as an alternative mechanism to realize it. This work highlights the engineering of copper oxidation states for manipulating the orbital current and its torque in the CuO$_x$-based heterostructures. The orbital hybridization and thus the orbital-Rashba-Edelstein effect at the CuO$_x$/Cu interfaces are significantly enhanced by increasing the copper oxidation state, yielding a torque efficiency that is almost ten times larger than the conventional heavy metals. The Cu$_4$O$_3$/Cu interface, rather than the widely accepted CuO/Cu interface, is revealed to account for the enhanced SOT performance in the CuO$_x$-based heterostructures. In addition, the torque efficiency can be alternatively switched between high and low thresholds through the redox reaction. The current results establish an exotic and robust strategy for engineering the orbital current and SOT for spin-orbitronics, which applies to other weak-SOC materials.