Acoustic waves could be the key to orbitronic devices

Since the discovery of electricity, countless advancements in technology have relied on harnessing the electron’s charge, which is the fundamental principle behind most of traditional electronics. Now, as conventional electronic devices approach their practical limits, scientists are turning their attention to manipulating other properties of the electron. For example, the harnessing of electron spin in the field of spintronics promises low-power computing by using spin currents to transfer information.

There is yet another untapped property in electrons, namely their orbital angular momentum. This property is the basis of ‘orbitronics,’ a new research frontier seeking to use the flow of orbital angular momentum (orbital currents) as a new medium for information transfer and device functionality. Despite the potential of orbitronics, there are not many practical and scalable ways to generate and control these orbital currents, and their generation mechanisms remain underexplored. Could sound waves hold the key to producing and controlling them?

To answer this question, a research team from Japan investigated the acoustic generation of orbital currents. This study, published in Volume 16 of the journal Nature Communications on August 29, 2025, was led by PhD student Mari Taniguchi and Professor Kazuya Ando from Keio University, Japan. Their paper explores two new physical phenomena—the acoustic orbital Hall effect and acoustic orbital pumping—that together establish a foundation for integrating sound technology with orbital physics.

The experiments focused on titanium (Ti)/nickel (Ni) bilayers, a material system known for its robust orbital response. The team fabricated Ti/Ni devices on a special substrate and used surface acoustic waves (SAWs), sound waves confined to the surface of a material, to excite its lattice dynamics. The use of Ti was key; since it has very weak spin-orbit coupling, any observed signal could be confidently attributed to the orbital degree of freedom rather than spin effects. The goal was to see if the mechanical vibration of the lattice could transfer its angular momentum to the electrons’ orbitals.

The researchers successfully observed the generation of orbital currents through two distinct acoustic mechanisms. First, they demonstrated acoustic orbital pumping, where a SAW-driven acoustic ferromagnetic resonance (a resonant precession of the magnetization) injected an orbital current from the Ni layer into the Ti layer. Second, they confirmed the generation of an acoustic orbital Hall effect. By measuring a DC voltage generated by a non-resonant SAW, they showed that the sound wave propagating in one direction generated an orbital current flowing perpendicular to it. This demonstrated that the lattice dynamics along the material’s surface are a direct and effective source of orbital current. Through systematic measurements and comparison with control samples, the researchers confirmed that the observed voltage signal was significantly larger than anything that could be attributed to the spin Hall effect. This conclusively proved the dominance of the orbital mechanism, validating their conclusion.

Taken together, these findings represent a key conceptual breakthrough, as Prof. Ando notes, “Since the orbital current was discovered only a few years ago, its generation mechanisms have remained largely unexplored. Recognizing the strong coupling between the orbital degree of freedom of electrons and the crystal lattice, we investigated and confirmed the possibility of generating orbital currents through phonons—the vibrations of the lattice.”

This work not only clarifies the nature of orbital currents arising in solids, but also lays the foundation for new design principles in future electronic devices. “Our study marks the first time that SAWs, which are already widely used in various electronic devices such as sensors, touch panels, and filter components, are linked to orbital currents. Thus, our findings open the door to new developments that integrate acoustic technology with orbitronics,” says Prof. Ando.

Future studies will focus on understanding the microscopic mechanisms behind the acoustic orbital Hall effect in greater detail and optimizing device architectures to generate orbital currents more reliably and efficiently. With any luck, this will accelerate the transition of orbitronics from a purely theoretical concept to next-generation technologies.

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About Keio University Global Research Institute (KGRI), Japan

The Keio University Global Research Institute (KGRI) was established in November 2016 as a research organization to bridge faculties and graduate schools across the university. KGRI aims to promote interdisciplinary and international collaborative research that goes beyond the boundaries of singular academic disciplines and international borders. It also aims to share research outcomes both in Japan and worldwide, further promoting engagement in joint research. To enhance those activities above, in 2022, Keio University set its goal of becoming a “Research university that forges the common sense of the future”.

Website: https://www.kgri.keio.ac.jp/en/index.html

About the Keio Institute of Pure and Applied Sciences

In commemoration of the 75^th anniversary of the Faculty of Science and Technology, Keio University has established the Keio Institute of Pure and Applied Sciences (KiPAS) as a new hub for fundamental research. Amid the accelerating advancement of science, technology, and social change, KiPAS is dedicated to deepening understanding of the fundamentals of science and engineering and promoting innovation grounded in these principles. By supporting exploratory and foundational research with potential for future development, and by inviting distinguished researchers from Japan and abroad, KiPAS aims to advance the frontiers of basic science and foster the next generation of world-class researchers.

Website: https://www.recsat.keio.ac.jp/kipas/

About Professor Kazuya Ando from Keio University

Prof. Kazuya Ando received his B.Eng. degree (2007), his M.S. degree in Engineering (2008), and his PhD degree (2010) from Keio University, Japan. He has served as an Associate Professor (2015–2025) before his promotion to full Professor in April 2025. He also served as a PRESTO Researcher at the Japan Science and Technology Agency from 2013 to 2017. Since 2020, he has been a Principal Investigator at the Keio Institute of Pure and Applied Sciences (KiPAS). His research interests include spintronics and orbitronics, with a particular focus on spin and orbital angular momentum transport in condensed matter systems.

https://scholar.google.com/citations?user=NjcBuuwAAAAJ&hl=en

https://www.k-ris.keio.ac.jp/html/100011426_en.html

https://researchmap.jp/kazuya-ando?lang=en

Funding information

This work was supported by JSPS KAKENHI (Grant Numbers: 22H04964, 20H00337, 20H02593), Spintronics Research Network of Japan (Spin-RNJ), MEXT Initiative to Establish Next-generation Novel Integrated Circuits Centers (X-NICS) (Grant Number: JPJ011438), JSPS KAKENHI (Grant Number: 23K13625), SSTF (Grant No. BA-1501-51), and the National Research Foundation of Korea (Grant No. RS-2024-00410027).