A unique propagation phenomenon of acoustic waves has been discovered, paving the way for developing advanced communication technologies using acoustic devices. The research was led by the Institute for Materials Research at Tohoku University, in collaboration with the Japan Atomic Energy Agency and the RIKEN Center for Emergent Matter Science.
Surface acoustic waves (SAWs) - elastic vibrations that travel along the surface of materials like ripples on a pond - play a crucial role in modern communication technologies. These are key components in frequency filters used in everyday devices such as mobile phones. These devices convert electrical signals into vibrations, or "ripples", through the piezoelectric effect, enabling efficient signal processing. Therefore, a deeper understanding of SAW behaviour is essential for advancing future technologies.
In the experiment, the team used advanced nanofabrication techniques to create a periodic array of nanoscale magnetic materials. The magnetic nanoscale array can be thought of as a specialized grating that the waves go through. To their surprise, instead of the typical symmetric diffraction pattern, the research team observed a completely novel, asymmetrical diffraction phenomenon of SAWs called "nonreciprocal diffraction."
"This phenomenon has previously been observed only in optics," remarks Yoichi Nii, "so we are very excited to confirm that it extends beyond optics to other wave phenomena."
Through theoretical analysis, the research team identified this asymmetrical behavior as arising from the unique interaction between SAWs and magnetic materials, specifically related to their angular momenta.
This finding may enable precise control of SAW propagation paths using magnetic fields, leading to the development of innovative acoustic devices that advance both classical and quantum communication technologies. Uncovering new properties of SAWs is essential for developing next-generation communication systems and devices.
The study was published in Physical Review Letters on January 14, 2025.
Physical Review Letters
10.1103/PhysRevLett.134.027001
Observation of Nonreciprocal Diffraction of Surface Acoustic Wave
14-Jan-2025