YoshiChika Otani

The coherent interaction between magnons and surface acoustic waves (SAWs) offers a powerful route for controlling magnetic dynamics, benefiting from the short wavelengths, low losses, and high integrability of SAWs in on-chip platforms. This review summarizes recent progress in SAW–magnon coupling, emphasizing selective and strong coupling regimes. Key parameters such as coupling strength and damping are discussed in relation to crystal and device symmetries that dictate magnon–phonon interactions. We highlight strategies for achieving selective coupling through spatial mode control, valley degrees of freedom in phononic superlattices, and symmetry engineering. Advances in device design have enabled the transition from weak to strong coupling, resulting in coherent energy exchange and hybridized magnon–phonon quasiparticles. Finally, emerging directions in nonlinear and non-Hermitian SAW–magnon dynamics, including exceptional points and frequency combs, are outlined as pathways toward next-generation magnonic and quantum information technologies.

Guided elastic waves are a truly cross-disciplinary key enabling technology. For more than five decades, surface acoustic wave (SAW) and bulk acoustic wave devices find widespread applications. Nowadays, different types of guided elastic waves cover the wide spectrum of applications spanning from quantum technologies to the life sciences, from controlling single excitations to macroscopic collective states in condensed matter. Six years after the first 2019 SAW roadmap, we believe it is time to make a step back and take a fresh look at the status of the field and its future challenges. Since the first roadmap in 2019, the spectrum clearly expanded and this new edition presents a current snapshot of the status of this vibrant field and prospects for potential future developments.

Spintronics has advanced memory and logic technologies by utilizing the electron's spin degree of freedom. In contrast, the electron's orbital angular momentum (OAM) was long regarded as quenched in transition metals due to crystal field effects and considered relevant only through spin–orbit coupling. Recent theoretical and experimental developments have overturned this view by revealing that Bloch states can host momentum-dependent orbital textures, enabling the generation and long-range transport of orbital currents even in light transition metals. This progress has given rise to the emerging field of orbitronics, which explores OAM as an active and tunable degree of freedom for information transfer and magnetization control. This review summarizes the fundamental mechanisms underlying orbitronics, including OAM generation via the orbital Hall effect and the orbital Rashba–Edelstein effect, the propagation and detection of orbital currents, and their conversion into efficient orbital torques on ferromagnets. We further highlight key experimental advances demonstrating long-range orbital transport and discuss how light-element materials can serve as effective orbital sources. Extending beyond electrons, we also examine the emergence of OAM in quasiparticles such as magnons and phonons, where twisted modes and valley pseudo-angular momentum reveal the universality of OAM physics. Together, these developments establish orbitronics as a new framework in condensed matter research, offering promising routes toward energy-efficient memory, logic, and sensing technologies.

The emerging field of orbitronics seeks to harness the orbital angular momentum (OAM) of electrons as an information carrier, offering new opportunities for next-generation memory and logic technologies. A central question for its viability is whether OAM currents can propagate efficiently across materials. Recent experiments have revealed highly nonlocal orbital transport phenomena, with characteristic lengths extending to several tens of nanometers—far beyond expectations based on conventional orbital quenching. These findings have fueled a theoretical debate with two opposing paradigms. One posits that genuine long-range transport arises from symmetry-protected hot spots in the electronic band structure, which preserve OAM coherence. The other contends that OAM currents are intrinsically short-lived, and that the observed long-range signatures originate instead from the local generation of orbital polarization by charge current gradients near boundaries. This perspective reviews the experimental evidence and theoretical foundations of both views, outlining the future research strategies needed to resolve this fundamental issue in orbitronics.

We report an unconventional twofold-symmetric magnetoelastic coupling in Ni films, mediated by Rayleigh surface acoustic waves (SAWs). This unique magnetoelastic symmetry originates from a dominant vertical shear strain ϵ_{yz}, which becomes prominent due to the low effective elastic modulus of Ni film. As the film thickness increases, ϵ_{yz} surpasses the conventional Rayleigh SAW strain ϵ_{xx}, a consequence originated from the elastic modulus mismatch at the film-substrate interface. This finding highlights the dominance of ϵ_{yz} in soft thin film under SAW excitation, offering a new platform to excite strong nonreciprocal and topological magnon-phonon hybridization.

The spin–orbit field and interfacial exchange field (IEF) are two major interface phenomena, and the detection and manipulation of these fields can enable a variety of nanoscale spintronics devices. Optimizing the IEF, which governs the spin-dependent scattering asymmetry at (ferromagnetic insulator)|(normal metal) interfaces, will pave the way for next-generation nanoscale, low-power insulator spintronics devices. Here, we demonstrate an experimental pathway to detect an IEF between insulating ferromagnet EuS and non-magnetic Cu using magnetoresistance (MR) measurements, and show that the spin-dependent scattering at the common interface can lead to a significant current-in-plane MR in Py | Cu | EuS trilayer Hall-bar device. Our experiment suggests that simple magnetoresistance measurements can be used to experimentally detect the IEF and thereby the magnetic state of a ferromagnetic insulator.