Long-range orbital transport and inverse orbital Hall effect in Co/Ru-based terahertz emitters

TL;DR

This paper demonstrates long-range orbital transport and enhanced terahertz emission in Co/Ru heterostructures, revealing the inverse orbital Hall effect and its potential for ultrafast spin-orbitronic devices.

Contribution

It provides the first experimental evidence of orbital-to-charge current conversion and long-range orbital transport in Co/Ru heterostructures, advancing the understanding of orbital transport mechanisms.

Findings

Orbital-to-charge current conversion observed in Co/Ru heterostructures.

Enhanced terahertz emission in Co/Pt/Ru trilayers due to constructive interference.

Strong correlation between damping and terahertz amplitude indicating efficient angular momentum conversion.

Abstract

The utilization of terahertz (THz) emission spectroscopy in femtosecond photoexcited spintronic heterostructures has emerged as a versatile tool for investigating ultrafast spin-transport in a noncontact and non-invasive manner. However, the investigation of ultrafast orbital-transport is still in the primitive stage. Here, we experimentally demonstrate the orbital-to-charge current conversion in Co/Ru heterostructures. Time-domain measurements reveal delayed and broadened terahertz waveforms with increasing Ru thickness, consistent with long-range orbital transport. In Co/Pt/Ru trilayers, the terahertz emission is further enhanced through constructive interference between the inverse spin Hall effect (ISHE) in Pt and inverse orbital Hall effect (IOHE) in Ru, while reversed stack structures show suppressed output. Ferromagnetic resonance (FMR) measurements reveal a strong correlation between damping and THz amplitude, highlighting efficient angular momentum conversion. These results position Co/Ru as a promising orbitronic platform for tunable ultrafast THz emission. Our results not only strengthen the physical mechanism of condensed matter physics but also pave the way for designing promising spin-orbitronic devices and terahertz emitters.