Significant orbit-to-charge conversion in CoFeB/Pt/SrIrO3 trilayer by terahertz emission spectroscopy

Orbitronics has been extensively explored theoretically and experimentally in orbital-charge conversion. The spin-charge conversion efficiency induced by the orbital Hall effect can be much larger than that of the spin Hall effect. However, orbitronics focuses primarily on light metal elements and their oxides, while exploring heavy metal elements and oxides is rare. In this Letter, we report significant enhancements in the ultrafast spin (orbit)-charge conversion for the CoFeB/Pt/SrIrO3 (SIO) trilayer using the terahertz emission spectroscopy, where the maximum enhancement calculated by the normalized terahertz emission amplitude is about three times that for the CoFeB/Pt bilayer. In addition, we observe a ∼2 orders of magnitude enhancement in the THz emission due to significant orbital transport in Pt-insertion heavy metal layer in the CoFeB/Pt/SIO heterostructure as compared to the CoFeB/SIO bilayer. Our findings not only demonstrate that the transition metals and their oxides exhibit strong inverse orbital Hall effect but also show that multilayer structures allow enhancing the spin-to-charge current conversion efficiency for THz applications, providing a direction to tailor THz emitters.