arXiv subjects

Hironari Isshiki

Publications and source records attributed to Hironari Isshiki.

7 recordsLinked to original sources

arXiv2026

Quasi-One-Dimensional Electronic Nature of Ta4SiTe4 Underlying the Giant Thermoelectric Performance

Ta4SiTe4 is a one-dimensional van der Waals material that exhibits an exceptionally large thermoelectric power factor below room temperature. However, since this material has been available only in the form of acicular microcrystals, experimental exploration of the electronic properties responsible for its giant thermoelectric performance has long been challenging. In this study, we quantitatively evaluated the one-dimensional electronic nature of Ta4SiTe4 by combining micro-spot angle-resolved photoemission spectroscopy and transport measurements on focused-ion-beam-processed samples. The angle-resolved photoemission spectroscopy measurements reveal anisotropic band dispersions along and perpendicular to the crystallographic c axis. Consistently, transport measurements demonstrate that the resistivity perpendicular to the c axis is approximately five times larger than that along the c axis at 200 K. These results provide direct experimental evidence for the quasi-one-dimensional electronic character of Ta4SiTe4, which underlies its giant thermoelectric response reported previously, and offer fundamental insights into the role of electronic dimensionality in enhancing thermoelectric performance.

cond-mat.mtrl-sci↗

arXiv2025

High-resolution magnetic imaging by mapping the locally induced anomalous Nernst effect using atomic force microscopy

We report a magnetic imaging method using atomic force microscopy to measure the locally induced anomalous Nernst effect. The tip contact creates a local temperature gradient on the sample surface controlled by a neighboring Joule heating wire. We demonstrate the imaging of magnetic domains in a nanowire of the ferromagnetic Weyl semimetal Co2MnGa with a spatial resolution of a sub-hundred nanometer at room temperature.

physics.app-ph↗

arXiv2025

Phenomenological model for the direct and inverse Edelstein effects

We have developed a phenomenological model that connects the direct and the inverse Edelstein effects. Our model implies a trade-off relation between the conversion coefficients for the direct and inverse effects. Thus, a large conversion coefficient for the inverse effect does not necessarily bring a large conversion coefficient for the direct effect. Instead of these coefficients, we propose a figure of merit of Edelstein effects which consists of two factors; one of them represents the magnitude of the spin-orbit coupling, and the other represents the strength of the hybridization between bulk and interface states. Both of them are quit important for the efficient conversion through Edelstein effects. To test our model, we measured the inverse and direct Edelstein effects at the Bi2O3/Cu interface using spin absorption method with a non-local spin valve structure and calculated the conversion coefficients. The effective spin Hall angle reaches ~0.09 in this system. This relatively large value is attributable to not only the large spin-orbit coupling but also the strong hybridization between the interface and bulk states at the Bi2O3/Cu interface.

cond-mat.mtrl-sci↗

arXiv2025

Observation of cluster magnetic octupole domains in the antiferromagnetic Weyl semimetal Mn3Sn nanowire

The antiferromagnetic Weyl semimetal Mn3Sn has attracted wide attention due to their vast anomalous transverse transport properties despite barely net magnetization. So far, the magnetic properties of Mn3Sn have been experimentally investigated on micrometer scale samples but not in nanometers. In this study, we measured the local anomalous Nernst effect of a (0001)-textured Mn3Sn nanowire using a tip-contact-induced temperature gradient with an atomic force microscope. Our approach directly provides the distribution of the cluster magnetic octupole moments in Mn3Sn with 80 nm spatial resolution, providing crucial information for integrating the Mn3Sn nanostructure into a memory device.

physics.app-ph↗

arXiv2025

Electrical detection of interfacial exchange field at the (ferromagnetic insulator)|(normal metal) interface using spin-dependent scattering

The spin-orbit field and interfacial exchange field are two major interface phenomena, and the detection and manipulation of these fields can enable a variety of nanoscale spintronics devices. Optimizing the interfacial exchange field, 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 interfacial exchange field between insulating ferromagnet EuS and non-magnetic Cu using magnetoresistance measurements, and show that the spin-dependent scattering at the common interface can lead to a significant current-in-plane magnetoresistance in Py$|$Cu$|$EuS trilayer Hall-bar device. Our experiment suggests that simple magnetoresistance measurements can be used to experimentally detect the interfacial exchange field and thereby the magnetic state of a ferromagnetic insulator.

cond-mat.mes-hall↗

arXiv2025

Nonlocal Electrical Detection of Reciprocal Orbital Edelstein Effect

Spin-Orbitronics leverages the spin and orbital degrees of freedom in solids for information processing. The orbital Edelstein effect and orbital Hall effect, where the charge current induces a nonequilibrium orbital angular momentum, offer a promising method to manipulate nanomagnets efficiently using light elements. Despite extensive research, understanding the Onsager reciprocity of orbital transport, fundamentally rooted in the second law of thermodynamics and time-reversal symmetry, remains elusive. In this study, we experimentally demonstrate the Onsager reciprocity of orbital transport in an orbital Edelstein system by utilizing nonlocal measurements. This method enables the precise identification of the chemical potential generated by orbital accumulation, avoiding the limitations associated with local measurements. Remarkably, we observe that the direct and inverse orbital-charge conversion processes produce identical electric voltages, confirming Onsager reciprocity in orbital transport. Additionally, we find that the orbital decay length, approximately 100 nm at room temperature, is independent of Cu thickness and decreases with lowering temperature, revealing a distinct contrast to spin transport behavior. Our findings provide valuable insights into both the reciprocity of the charge-orbital interconversion and the nonlocal correlation of orbital degree of freedom, laying the ground for orbitronics devices with long-range interconnections.

cond-mat.mes-hall↗

arXiv2023

Strongly Coupled Spin Waves and Surface Acoustic Waves at Room Temperature

Here, we report the observation of strong coupling between magnons and surface acoustic wave (SAW) phonons in a thin CoFeB film constructed in an on-chip SAW resonator by analyzing SAW phonon dispersion anticrossings. Our device design provides the tunability of the film thickness with a fixed phonon wavelength, which is a departure from the conventional approach in strong magnon--phonon coupling research. We detect a monotonic increase in the coupling strength by expanding the film thickness, which agrees with our theoretical model. Our work offers a significant way to advance fundamental research and the development of devices based on magnon--phonon hybrid quasiparticles.

cond-mat.mes-hall↗