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
Renyou Xu, Xiaobai Ning, Houyi Cheng, Yuxuan Yao, Zejun Ren, Shaojie Liu, Mingcong Dai, Yong Xu, Sai Li, Ao Du, Xiaojun Wu, Fengxia Hu, Baogen Shen, Jirong Sun, Hui Zhang, Weisheng Zhao
Abstract
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.