Inverse orbital Hall effect induced terahertz emission enabled by a ferromagnet with quenched orbital moment in Fe/Pt/W trilayers

TL;DR

This study demonstrates that Fe/Pt/W trilayers exhibit enhanced terahertz emission via the inverse orbital Hall effect, revealing orbital angular momentum transport as a key mechanism even in materials with quenched orbital moments.

Contribution

It uncovers the significant role of the inverse orbital Hall effect in THz emission from Fe-based heterostructures, challenging the assumption that quenched orbital moments suppress orbital contributions.

Findings

Enhanced THz emission in Fe/Pt/W trilayers.

Orbital angular momentum transport dominates in the trilayer.

Long-distance signal persistence and pulse broadening observed.

Abstract

The inverse orbital Hall effect (IOHE) has recently attracted considerable attention as an emerging mechanism for terahertz (THz) emission based on ultrafast angular-momentum-to-charge conversion. Most experimental studies have focused on materials with strong spin-orbit coupling or pronounced orbital character, where sizable orbital Hall responses are expected. Elemental ferromagnets such as Fe are generally regarded as quenched orbital sources and are not expected to exhibit orbital-dominated THz emission. Here, we report a pronounced enhancement of THz emission in Fe/Pt/W trilayer heterostructures, despite the absence of detectable orbital contributions in the corresponding Fe/Pt and Fe/W bilayers. Thickness-dependent measurements reveal long-distance signal persistence, systematic delay accumulation, and pronounced pulse broadening with increasing W thickness. These features are inconsistent with diffusive spin transport and indicate that orbital angular momentum transport in the W layer, converted into charge current via the IOHE, becomes a dominant channel for THz emission in the trilayer configuration. Our results demonstrate that strong IOHE can emerge in heterostructures incorporating a quenched orbital ferromagnet, providing an effective route to enhance spintronic THz emitters through orbital Hall physics.