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H. Yoshikawa

Publications and source records attributed to H. Yoshikawa.

15 recordsLinked to original sources
arXiv2026

Generalized Helicity-Dependent Magnetization Switching via Substrate Phonons

Coherent excitation of circularly-polarized substrate phonons can drive deterministic reversal of magnetization in an adjacent magnetic layer. However, the extent to which this substrate-mediated mechanism can be generalized across different materials remains unresolved. Here, we measure and compare the spectral dependence of helicity-dependent magnetization reversal in magnetic GdFeCo layers grown on a diverse set of diamagnetic substrates. Switching is observed for all investigated substrates, spanning six point groups and several infrared-active transverse-optical phonon symmetries. While the switching spectra broadly overlap with the Reststrahlen bands, their maxima are systematically shifted to wavelengths shorter than the corresponding transverse-optical phonon resonances. This spectral mismatch shows that substrate absorption alone does not determine the switching efficiency. Transfer-matrix calculations show that strong absorption concentrates energy deposition near the substrate interface, providing a possible source of local heating that could suppress magnetization reversal. Our results reveal the broad applicability of substrate-mediated phononic switching while showing that its efficiency is governed by the full optical response of the heterostructure rather than substrate absorption alone.

cond-mat.mtrl-sci↗
arXiv2024

Circular polarization measurement for individual gamma rays in capture reactions with intense pulsed neutrons

Measurements of circular polarization of $γ$-ray emitted from neutron capture reactions provide valuable information for nuclear physics studies. The spin and parity of excited states can be determined by measuring the circular polarization from polarized neutron capture reactions. Furthermore, the $γ$-ray circular polarization in a neutron capture resonance is crucial for studying the enhancement effect of parity nonconservation in compound nuclei. The $γ$-ray circular polarization can be measured using a polarimeter based on magnetic Compton scattering. A polarimeter was constructed, and its performance indicators were evaluated using a circularly polarized $γ$-ray beam. Furthermore, as a demonstration, the $γ$-ray circular polarization was measured in $^{32}$S($\vec{\textrm{n}}$,$γ$)$^{33}$S reactions with polarized neutrons.

physics.ins-det↗
arXiv2024

Transverse asymmetry of individual $γ$-rays in the $^{139}$La($\vec{n}$, $γ$)$^{140}$La reaction

The enhancement of the parity-violating asymmetry in the vicinity of $p$-wave compound nuclear resonances was observed for a variety of medium-heavy nuclei. The enhanced parity-violating asymmetry can be understood using the $s$-$p$ mixing model. The $s$-$p$ mixing model predicts several neutron energy-dependent angular correlations between the neutron momentum $\vec k_n$, neutron spin $\vecσ_n$, $γ$-ray momentum $\vec k_γ$, and $γ$-ray polarization $\vecσ_γ$ in the $(n,γ)$ reaction. In this paper, the improved value of the transverse asymmetry of $γ$-ray emissions, corresponding to a correlation term $\vecσ_n\cdot(\vec k_n\times\vec k_γ)$ in the $^{139}\mathrm{La}(\vec n,γ)^{140}\mathrm{La}$ reaction, and the transverse asymmetries in the transitions to several low excited states of $^{140}\mathrm{La}$ are reported.

nucl-ex↗
arXiv2023

Spin dependence in the $p$-wave resonance of ${^{139}\vec{\rm{La}}+\vec{n}}$

We measured the spin dependence in a neutron-induced $p$-wave resonance by using a polarized epithermal neutron beam and a polarized nuclear target. Our study focuses on the 0.75~eV $p$-wave resonance state of $^{139}$La+$n$, where largely enhanced parity violation has been observed. We determined the partial neutron width of the $p$-wave resonance by measuring the spin dependence of the neutron absorption cross section between polarized $^{139}\rm{La}$ and polarized neutrons. Our findings serve as a foundation for the quantitative study of the enhancement effect of the discrete symmetry violations caused by mixing between partial amplitudes in the compound nuclei.

nucl-ex↗
arXiv2022

Angular distribution of $γ$-rays from a neutron-induced $p$-wave resonance of $^{132}$Xe

A neutron-energy dependent angular distribution was measured for individual $γ$-rays from the 3.2 eV $p$-wave resonance of $^{131}$Xe+$n$, that shows enhanced parity violation owing to a mixing between $s$- and $p$-wave amplitudes. The $γ$-ray transitions from the $p$-wave resonance were identified, and the angular distribution with respect to the neutron momentum was evaluated as a function of the neutron energy for 7132 keV $γ$-rays, which correspond to a transition to the 1807 keV excited state of $^{132}$Xe. The angular distribution is considered to originate from the interference between $s$- and $p$-wave amplitudes, and will provide a basis for a quantitative understanding of the enhancement mechanism of the fundamental parity violation in compound nuclei.

nucl-ex↗
arXiv2022

Regulating electron diffraction direction with cylindrically symmetric rotating crystal

We report a promising InSiO film that allows simultaneous observation of sample morphology and Kikuchi patterns in raster scan mode of scanning electron microscopy. This new experimental observation suggests potential mechanism beyond existing diffraction theories. We find by simulation that this material has a novel cylindrically symmetric rotational crystalline structure that can control the diffraction direction of electrons through a specific rotational distribution of crystal planes, while being independent of the angle and energy of incident electrons within a certain range.

cond-mat.mtrl-sci↗
arXiv2022

Measurement of the transverse asymmetry of $γ$-rays in the $^{117}$Sn(n,$γ$)$^{118}$Sn reaction

Largely enhanced parity-violating effects observed in compound resonances induced by epithermal neutrons are currently attributed to the mixing of parity-unfavored partial amplitudes in the entrance channel of the compound states. Furthermore, it is proposed that the same mechanism that enhances the parity-violation also enhances the breaking of time-reversal-invariance in the compound nucleus. The entrance-channel mixing induces energy-dependent spin-angular correlations of individual $γ$-rays emitted from the compound nuclear state. For a detailed study of the mixing model, a $γ$-ray yield in the reaction of $^{117}$Sn(n,$γ$)$^{118}$Sn was measured using the pulsed beam of polarized epithermal neutrons and Ge detectors. An angular dependence of asymmetric $γ$-ray yields for the orientation of the neutron polarization was observed.

nucl-ex↗
arXiv2022

Banach fixed-point between SEM image and EBSD diffraction pattern from a cylindrically symmetric rotating crystal

The Kikuchi bands arise from Bragg diffraction of incoherent electrons scattered within a crystalline specimen and can be observed in both the transmission and reflection modes of scanning electron microscopy (SEM). Converging, rocking, or grazing incidence beams must be used to generate divergent electron sources to obtain the Kikuchi pattern. This paper report the observation of Kikuchi pattern from SEM images of an exceptional rotating crystal with continuous rotation in the local crystal direction and satisfying cylindrical symmetry, named a cylindrically symmetric rotating crystal. SEM images of cylindrically symmetric rotating crystals reflect the interactions between electrons and the sample in both the real- and momentum-space. Furthermore, we identify an unexpected mathematical relationship between the electron backscattered diffraction (EBSD) Kikuchi pattern matrix map and the SEM image of the present sample which can be rationalized as a concrete example of the Banach fixed-point theorems in the field of EBSD technique.

cond-mat.mtrl-sci↗
arXiv2022

Angular distribution of $γ$ rays from the p-wave resonance of $^{118}$Sn

The neutron energy-dependent angular distribution of $γ$ rays from $^{117}{\rm Sn}(n,γ)$ reaction was measured with germanium detectors and a pulsed neutron beam. The angular distribution was clearly observed in $γ$-ray emissions with an energy of 9327 keV which corresponds to the transition from a neutron resonance of $^{117}{\rm Sn}+n$ to the ground state of $^{118}{\rm Sn}$. The angular distribution causes an angular-dependent asymmetric resonance shape. An asymmetry $A_{\rm LH}$ was defined as $(N_{\rm L}-N_{\rm H})/(N_{\rm L}+N_{\rm H})$, where $N_{\rm L}$ and $N_{\rm H}$ are integrated values for lower- and higher-energy regions of a neutron resonance, respectively. We found that the $A_{\rm LH}$ has the angular dependence of $(A \cos θ_γ+B)$, where $θ_γ$ is the $γ$-ray emission angle with respect to the incident neutron momentum, with $A=0.394 \pm 0.073$ and $B = 0.118 \pm 0.029$ in the 1.33 eV p-wave resonance.

nucl-ex↗
arXiv2021

Measurement of nuclear spin relaxation time in lanthanum aluminate for development of polarized lanthanum target

The nuclear spin-lattice relaxation time ($T_1$) of lanthanum and aluminum nuclei in a single crystal of lanthanum aluminate doped with neodymium ions is studied to estimate the feasibility of the dynamically polarized lanthanum target applicable to beam experiments. The application of our interest is the study of fundamental discrete symmetries in the spin optics of epithermal neutrons. This study requires a highly flexible choice of the applied magnetic field for neutron spin control and favors longer $T_1$ under lower magnetic field and at higher temperature. The $T_1$ of $^{139}{\rm La}$ and ${}^{27}{\rm Al}$ was measured under magnetic fields of $0.5$-$2.5$ T and at temperatures of $0.1$-$1.5$ K and found widely distributed up to 100 h. The result suggests that the $T_1$ can be as long as $T_1 \sim$ 1 h at $0.1$ K with a magnetic field of $0.1$ T, which partially fulfills the requirement of the neutron beam experiment. Possible improvements to achieve a longer $T_1$ are discussed.

physics.ins-det↗
arXiv2021

Energy dependent angular distribution of individual $γ$-rays in the $^{139}$La($n$, $γ$)$^{140}$La* reaction

Neutron energy-dependent angular distributions were observed for individual $γ$-rays from the 0.74 eV p-wave resonance of $^{139}$La+$n$ to several lower excited states of $^{140}$La. The $γ$-ray signals were analyzed in a two dimensional histogram of the $γ$-ray energy, measured with distributed germanium detectors, and neutron energy, determined with the time-of-flight of pulsed neutrons, to identify the neutron energy dependence of the angular distribution for each individual $γ$-rays. The angular distribution was also found for a photopeak accompanied with a faint p-wave resonance component in the neutron energy spectrum. Our results can be interpreted as interference between s- and p-wave amplitudes which may be used to study discrete symmetries of fundamental interactions.

nucl-ex↗
arXiv2018

Laser-induced antiferromagnetic-like resonance in amorphous ferrimagnets

The magnetization dynamics for ferrimagnets at the angular momentum compensation temperature T_A is believed to be analogous to that for antiferromagnets. We investigated the pulsed-laser-induced magnetization dynamics in amorphous rare-earth transition-metal ferrimagnet films with a T_A just above room temperature. For a low pulse fluence, the magnetization precession frequency decreases as the applied magnetic field increases, whereas for a higher pulse fluence, it increases as the applied field increases. The result was well explained by the left-handed and right-handed precession modes of the antiferromagnetic-like resonance at temperatures below and above T_A, respectively, and the data were in agreement with the theoretical simulation. The study demonstrated the experimental route to achieving antiferromagnetic resonance in ferrimagnets using a pulsed laser.

cond-mat.mtrl-sci↗
arXiv2011

Coupled Oscillator Model of the Business Cycle with Fluctuating Goods Markets

The sectoral synchronization observed for the Japanese business cycle in the Indices of Industrial Production data is an example of synchronization. The stability of this synchronization under a shock, e.g., fluctuation of supply or demand, is a matter of interest in physics and economics. We consider an economic system made up of industry sectors and goods markets in order to analyze the sectoral synchronization observed for the Japanese business cycle. A coupled oscillator model that exhibits synchronization is developed based on the Kuramoto model with inertia by adding goods markets, and analytic solutions of the stationary state and the coupling strength are obtained. We simulate the effects on synchronization of a sectoral shock for systems with different price elasticities and the coupling strengths. Synchronization is reproduced as an equilibrium solution in a nearest neighbor graph. Analysis of the order parameters shows that the synchronization is stable for a finite elasticity, whereas the synchronization is broken and the oscillators behave like a giant oscillator with a certain frequency additional to the common frequency for zero elasticity.

q-fin.ST↗
arXiv2001

A Control System of the Joint-Project Accelerator Complex

The current status of the control system for a new high intensity proton accelerator, the JAERI-KEK Joint Project, is presented. The Phase 1 of the Joint-Project has been approved and recently started its construction at JAERI site at Tokai. The first beam commissioning is scheduled in 2006. In parallel with it, a 60-MeV Linac is now being constructed at KEK site at Tsukuba for R&D purpose. Recently the Project has officially decided to use the Experimental Physics and Industrial Control System (EPICS). Under the EPICS environment, we are challenging to implement the Ethernet/IP network for all communication, even at the level of end-point controllers which are so far connected via a field bus. In order to realize such a system, three new controllers (PLCs, WE7000 stations and general-purpose Ethernet boards) are being developed. A prototype EPICS driver for the PLCs works fine and is used to control the ion-source at the KEK Linac.

physics.acc-ph↗