arXiv subjects

Ryusuke Hisatomi

Publications and source records attributed to Ryusuke Hisatomi.

14 recordsLinked to original sources

arXiv2026

Coexistence of Magnon-Induced Optical Vortex and Gaussian Beam Scattering Assisted by Rotational Umklapp Process

The exploitation of crystal-lattice symmetries to engineer angular momentum transfer between structured light and magnons marks a novel frontier for optomagnonic research. In Brillouin light scattering, when focused light propagates parallel to an external magnetic field and interacts with ferromagnetic uniform magnons, only optical-vortex scattering is expected to be permitted. Due to the combined effects of magneto-optical coupling and optical spin-orbit interaction, the transfer of magnon spin angular momentum to photon orbital angular momentum allows for this distinctive scattering phenomenon. Here, we experimentally demonstrate that, for a specific ferromagnetic crystal orientation, Gaussian-beam scattering coexists with the optical-vortex scattering, contrary to conventional expectations based on angular momentum conservation between magnons and photons. We show that the crystal lattice, via the rotational Umklapp process, provides the missing angular momentum required for the Gaussian-beam scattering. Furthermore, we predict that as the degree of light focusing increases, the relative efficiencies of the Gaussian-beam and optical-vortex scattering processes reverse.

physics.optics↗

arXiv2026

Focusing Surface-Acoustic-Wave Resonators on Thin-Film Lithium Niobate with Transverse-Mode Suppression

Surface-acoustic-wave (SAW) resonators are a promising platform for constructing hybrid quantum systems, where confined acoustic waves enable strong interaction with various physical systems. Focusing SAW resonators, reducing mode volume while suppressing diffraction losses, have recently been investigated for application in such hybrid systems. However, the resonator leads to additional transverse-mode resonances, which cause undesired responses. In this work, we develop focusing SAW resonators on a thin-film lithium niobate on sapphire. A film thinner than the SAW wavelength allows a highly confined acoustic-wave mode to be localized on the substrate surface. By using contoured electrodes following a two-dimensional Gaussian beam shape, we make the SAW mode focused to nearly a diffraction-limited and confirm it via optical imaging. Furthermore, by engineering the spatial mode overlap of the interdigital transducer electrodes, we suppress the excitation of higher-order transverse modes.

quant-ph↗

arXiv2025

Optical vortex generation by magnons with spin-orbit-coupled light

Light possesses both spin and orbital angular momentum. In spatially asymmetric optical fields, these properties undergo spontaneous coupling, referred to as optical spin-orbit coupling. The study of the coupling has recently become central in modern optics due to its substantial applications in communications, sensing, and quantum control. A key challenge is to clarify the relationship between the origins of spatially asymmetric optical fields and the resulting spin-orbit coupling. Current research focuses on materials and configurations exhibiting spatial asymmetry, such as focusing lenses, interfaces, inhomogeneous media, and metasurfaces. However, Maxwell's equations indicate that matter can introduce both spatial and temporal asymmetry into optical fields. For instance, magnetic ordering breaks the time-reversal symmetry of interacting optical fields via the magneto-optic effect, introducing nonreciprocity in the resulting optical phenomena. Despite the importance, optical phenomena involving both spatially and temporally asymmetric optical fields remain unexplored. Here, we demonstrate that breaking time and spatial symmetries through magnons and light focusing, respectively, transforms an input Gaussian beam into a specific optical vortex beam in a nonreciprocal manner. This phenomenon is quantitatively explained by integrating the physics of magnon-induced Brillouin light scattering with optical spin-orbit coupling. The observed conservation of total angular momentum, encompassing both magnons and photons, further indicates that magnons can control both spin and orbital angular momentum of light. Finally, we outline future research directions enabled by asymmetric optical fields in both space and time.

physics.optics↗

arXiv2025

Néel vector rotation driven by spin-orbit torque in amorphous ferrimagnetic GdCo

Spin superfluidity, a phenomenon enabling low dissipative spin transport analogous to superfluidity in liquid helium and superconductivity in electronic systems, has remained a theoretical concept. To realize the spin superfluidity in an antiferromagnet, it is necessary to excite a Néel vector rotation within the magnetic easy-plane, which has been elusive so far. In this study, we demonstrated spin-orbit torque-driven Néel vector rotation in amorphous ferrimagnetic GdCo. A pseudo-magnetic easy-plane is formed in a spin-flop state under an external magnetic field at the vicinity of the magnetization compensation temperature, and we observed stochastic binary switching in the anomalous Hall resistance, directly attributed to Néel vector rotation. Furthermore, homodyne detection confirmed rotation frequencies in the GHz range as expected from atomic spin simulations, providing evidence of dynamic Néel vector behavior. These findings represent a crucial advance towards the realization of spin superfluidity.

cond-mat.mtrl-sci↗

arXiv2024

Spin current generation by acousto-electric evanescent wave

We experimentally demonstrate that a spin current can be induced by the acousto-electric evanescent wave, an electric field associated with surface acoustic waves (SAWs) that decay along the surface normal. A previous study showed that a magnetic-field-dependent dc voltage (acoustic voltage) emerges in heavy metal (HM)/ferromagnet (FM) bilayers under excitation of SAWs. The effect, referred to as the acoustic spin Hall effect, was understood by assuming a SAW-induced ac spin current rectified by the oscillation of the FM layer magnetization and the inverse spin Hall effect. However, the mechanism of the spin current generation remained unidentified. Here we measure the acoustic voltage as a function of the SAW propagation direction relative to the crystalline orientation of a LiNbO$_3$ substrate. We find that the magnetic field angle dependence of the acoustic voltage exhibits a phase shift depending on the SAW propagation direction. The result is consistently explained in terms of the acousto-electric evanescent wave generating the spin current in HM layer via the spin Hall effect, thus clarifies the origin of the acoustic spin Hall effect.

cond-mat.mes-hall↗

arXiv2024

Electromagnetic evanescent field associated with surface acoustic wave: Response of metallic thin films

Surface acoustic waves (SAWs), coherent vibrational modes localized at solid surfaces, have been employed to manipulate and detect electronic and magnetic states in condensed-matter systems via strain. SAWs are commonly excited in a piezoelectric material, often the substrate. In such systems, SAWs not only generate strain but also electric field at the surface. Conventional analysis of the electric field accompanying the SAW invokes the electrostatic approximation, which may fall short in fully capturing its essential characteristics by neglecting the effect of the magnetic field. Here we study the electric and magnetic fields associated with SAWs without introducing the electrostatic approximation. The plane wave solution takes the form of an evanescent field that decays along the surface normal with a phase velocity equal to the speed of sound. If a metallic film is placed on the piezoelectric substrate, a time- and space-varying electric field permeates into the film with a decay length along the film normal defined by the skin depth and the SAW wavelength. For films with high conductivity, the phase of the electric field varies along the film normal. The emergence of the evanescent field is a direct consequence of dropping the electrostatic approximation, providing a simple but critical physical interpretation of the SAW-induced electromagnetic field.

cond-mat.mes-hall↗

arXiv2024

Quantitative evaluation method for magnetoelastic coupling between surface acoustic waves and spin waves using electrical and optical measurements

Coupling and hybridization of different elementary excitations leads to new functionalities. In phononics and spintronics, magnetoelastic coupling between Rayleigh-type surface acoustic wave (SAW) and spin wave (SW) has recently attracted much attention. Quantitatively evaluating and comparing the coupled system are essential to develop the study of the magnetoelastic SAW-SW coupling. So far, previous studies of SAW-SW coupling have employed a quantity called coupling strength. However, it is still challenging to compare the coupling strength values among studies fairly because the quantity depends on the device geometry and the applied magnetic field angle, which are not unified among the previous studies. Here, we focus on a practical constant composed of a magnetoelastic constant and a strain amplitude that depends only on the material properties. We demonstrate a versatile evaluation technique to evaluate the practical constant by combining electrical measurements and optical imaging. An essential part of the technique is an analysis that can be used under off-resonance conditions where SAW and SW resonance frequencies do not match. Existing analysis can only handle the case under on-resonance conditions. Our analysis makes it possible to observe the magnetoelastic couplings between SAW with resonance frequencies that can be imaged optically and SW with resonance frequencies in the gigahertz range. Our demonstrated technique, which uses electrical and optical measurements under off-resonance conditions, can significantly advance research on SAW-SW coupled systems.

cond-mat.mes-hall↗

arXiv2024

Handedness manipulation of propagating antiferromagnetic magnons

Antiferromagnetic magnons possess a distinctive feature absent in their ferromagnetic counterparts: the presence of two distinct handedness modes, the right-handed (RH) and left-handed (LH) precession modes. The magnon handedness determines the sign of spin polarization carried by the propagating magnon, which is indispensable for harnessing the diverse functionalities. However, the control of coherently propagating magnon handedness in antiferromagnets has remained elusive so far. Here we demonstrate the manipulation and electrical readout of propagating magnon handedness in perpendicularly magnetized synthetic antiferromagnets (SAF). We find that the antiferromagnetic magnon handedness can be directly identified by measuring the inverse spin Hall effect (ISHE) voltage, which arises from the spin pumping effect caused by the propagating antiferromagnetic magnons in the SAF structure. The RH and LH modes of the magnon can be distinguishable particularly when the SAF structure is sandwiched by heavy metals with the same sign of spin Hall angle. Moreover, we succeed in controlling the handedness of propagating antiferromagnetic magnons by tuning the excitation microwave frequency. This work unveils promising avenues for harnessing magnon unique properties in antiferromagnet-based magnonic applications.

cond-mat.mtrl-sci↗

arXiv2023

Quantitative optical imaging method for surface acoustic waves using optical path modulation

A Rayleigh-type surface acoustic wave (SAW) is used in various fields as classical and quantum information carriers because of its surface localization, high electrical controllability, and low propagation loss. Coupling and hybridization between the SAW and other physical systems such as magnetization, electron charge, and electron spin are the recent focuses in phononics and spintronics. A precise measurement of the surface wave amplitude is often necessary to discuss the coupling strengths. However, there are only a few such measurement techniques and they generally require a rather complex analysis. Here we develop and demonstrate a straightforward measurement technique that can quantitatively characterize the SAW. The technique optically detects the surface waving due to the coherently driven SAW by the optical path modulation. Furthermore, when the measurement system operates in the shot-noise-limited regime, the surface slope and displacement at the optical spot can be deduced from the optical path modulation signal. Our demonstrated technique will be an important tool for SAW-related research.

physics.app-ph↗

arXiv2021

Optical polarimetric measurement of surface acoustic waves

Surface acoustic wave (SAW) is utilized in diverse fields ranging from physics, engineering, to biology, for transducing, sensing and processing various signals. Optical measurement of SAW provides valuable information since the amplitude and the phase of the displacement field can be measured locally with the resolution limited by the spot size of the optical beam. So far, optical measurement techniques rely on modulation of optical path, phase, or diffraction associated with SAW. Here, we demonstrate that SAW can be measured with an optical polarimeter. We show that the slope of the periodically tilting surface due to the coherently driven SAW is translated into the angle of polarization rotation, which can be straightforwardly calibrated when polarimeters work in the shot-noise-limited regime. The polarimetric measurement of SAW is thus beneficial for quantitative studies of SAW-based technologies.

physics.app-ph↗

arXiv2021

Magnon-exciton proximity coupling at a van der Waals heterointerface

Spin and photonic systems are at the heart of modern information devices and emerging quantum technologies. An interplay between electron-hole pairs (excitons) in semiconductors and collective spin excitations (magnons) in magnetic crystals would bridge these heterogeneous systems, leveraging their individual assets in novel interconnected devices. Here, we report the magnon-exciton coupling at the interface between a magnetic thin film and an atomically-thin semiconductor. Our approach allies the long-lived magnons hosted in a film of yttrium iron garnet (YIG) to strongly-bound excitons in a flake of a transition metal dichalcogenide, MoSe$_2$. The magnons induce on the excitons a dynamical valley Zeeman effect ruled by interfacial exchange interactions. This nascent class of hybrid system suggests new opportunities for information transduction between microwave and optical regions.

cond-mat.mes-hall↗

arXiv2020

Optical heterodyne imaging of magnetostatic modes in one-dimensional magnonic crystals

We demonstrate a real-space imaging of a heterodyne signal of light that is produced as a result of the Brillouin light scattering by coherently driven magnons in magnetostatic modes. With this imaging technique, we characterize surface magnetostatic modes (Damon-Eshbach modes) in a one-dimensional magnonic crystal, which is formed by patterned aluminum strips deposited on the ferromagnetic film. The modified band structures of the magnonic crystal are deduced from the Fourier transforms of the real-space images. The heterodyne imaging provides a simple and powerful method to probe magnons in structured ferromagnetic films, paving a way to investigate more complex phenomena, such as Anderson localization and topological transport with magnons.

cond-mat.mes-hall↗

arXiv2019

Resonant magnetic induction tomography of a magnetized sphere

We demonstrate the structural imaging of magnetostatic spin-wave modes hosted in a millimeter-sized ferromagnetic sphere. Unlike for low-dimensional magnetic materials, there is no prior technique to image these modes in bulk magnetized solid of revolution. Based on resonant magnetic induction tomography in the microwave range, our approach ensures the robust identification of these non-trivial spin-wave modes by establishing their azimuthal and polar dependences, starting point of magnonic fundamental studies and hybrid systems with complex spin textures well beyond the uniform precession mode.

cond-mat.mtrl-sci↗

arXiv2016

Bidirectional conversion between microwave and light via ferromagnetic magnons

Coherent conversion of microwave and optical photons in the single-quantum level can significantly expand our ability to process signals in various fields. Efficient up-conversion of a feeble signal in the microwave domain to the optical domain will lead to quantum-noise-limited microwave amplifiers. Coherent exchange between optical photons and microwave photons will also be a stepping stone to realize long-distance quantum communication. Here we demonstrate bidirectional and coherent conversion between microwave and light using collective spin excitations in a ferromagnet. The converter consists of two harmonic oscillator modes, a microwave cavity mode and a magnetostatic mode called Kittel mode, where microwave photons and magnons in the respective modes are strongly coupled and hybridized. An itinerant microwave field and a travelling optical field can be coupled through the hybrid system, where the microwave field is coupled to the hybrid system through the cavity mode, while the optical field addresses the hybrid system through the Kittel mode via Faraday and inverse Faraday effects. The conversion efficiency is theoretically analyzed and experimentally evaluated. The possible schemes for improving the efficiency are also discussed.

quant-ph↗