Terahertz generation via the inverse orbital Rashba-Edelstein effect at the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">Ni</mml:mi><mml:mtext>/</mml:mtext><mml:mi>Cu</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mi>x</mml:mi></mml:msub></mml:mrow></mml:math> interface

Orbitronics provides novel mechanisms to generate terahertz (THz) emission using the orbital angular momentum of electrons. Here, we report a systematic investigation of the THz emission from <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi mathvariant="normal">Ni</a:mi><a:mtext>/</a:mtext><a:mi>Cu</a:mi><a:msub><a:mi mathvariant="normal">O</a:mi><a:mi>x</a:mi></a:msub></a:mrow></a:math> heterostructures pumped by a femtosecond laser pulse. Despite the very weak spin-orbit coupling of <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:mi>Cu</d:mi><d:msub><d:mi mathvariant="normal">O</d:mi><d:mi>x</d:mi></d:msub></d:mrow></d:math>, considerable THz radiation from <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mrow><f:mi mathvariant="normal">Ni</f:mi><f:mtext>/</f:mtext><f:mi>Cu</f:mi><f:msub><f:mi mathvariant="normal">O</f:mi><f:mi>x</f:mi></f:msub></f:mrow></f:math> has been observed, with a polarity state that is magnetically controllable and the intensity as much as about 20% of that found in Ni/Pt spintronic THz emitter. We find conclusive evidence that THz radiation stems from the inverse orbital Rashba-Edelstein effect at the <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:mrow><i:mi mathvariant="normal">Ni</i:mi><i:mtext>/</i:mtext><i:mi>Cu</i:mi><i:msub><i:mi mathvariant="normal">O</i:mi><i:mi>x</i:mi></i:msub></i:mrow></i:math> interface, which can be manipulated by tuning oxygen-induced orbital hybridization. Our experimental results of Ni thickness-dependent THz emission, combined with theoretical modeling, reveal long-range diffusion-length characteristics of orbital current within the Ni layer. This work enhances the understanding of the THz emission mechanism based on orbital-to-charge conversion, providing guidance for the development of orbitronic THz emitters.