Orbital-related transport and inverse orbital Hall effect in Co/Ru-based terahertz emitters
Phys. Rev. B 114, 094421 – Published 19 August, 2026
DOI: https://doi.org/10.1103/g4mc-zf7p
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 noninvasive 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 and identify signatures that cannot be consistently explained within a conventional spin-current framework. Time-domain measurements reveal delayed and broadened THz waveforms with increasing Ru thickness, suggesting the presence of long-range angular momentum transport associated with orbital contributions. In Co/Pt/Ru trilayers, the THz emission is further enhanced through cooperative effects between the inverse spin Hall effect (ISHE) in Pt and inverse orbital Hall effect (IOHE) in Ru, where collinear charge currents are generated and add constructively. In contrast, reversed stacking configurations exhibit suppressed emission, highlighting the critical role of stacking sequence and interface-controlled transmission. 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 THz emitters.
