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A. Ikeda

Publications and source records attributed to A. Ikeda.

At least 19 recordsLinked to original sources
arXiv2026

Compact nondestructive generator for microsecond-class ultrafast pulsed magnetic fields

The sweep rate of pulsed magnetic fields is a key factor in exploring of nonequilibrium phenomena in matter. However, the nondestructive generation of ultrafast pulsed magnetic fields is challenging because of the large time constants associated with the large inductance and capacitance of conventional pulsed magnetic field generators, as well as the residual inductance of the power devices and the system itself. We have developed a new compact pulsed magnetic field generator using commercially available state-of-the-art ultrafast power devices, enabling the generation of ultrafast pulsed magnetic fields up to approximately 1 T with a pulse duration of 3.8 $\mu$s. We present the performance of the newly developed system and compare the experimentally obtained magnetic field waveforms with the results of a simple circuit simulation. In addition, we demonstrate magnetization measurements on cobalt powder and Faraday rotation measurements on CdS single crystal using the developed system.

physics.ins-det↗
arXiv2025

Complex single-site magnetism and magnetotransport in single-crystalline Gd$_{2}$AlSi$_{3}$

We present a detailed investigation of single-crystal samples of the magnetic compound Gd$_{2}$AlSi$_{3}$, which crystallizes in the $α$-ThSi$_2$ type tetragonal structure. We report the temperature and magnetic field dependence of the magnetic susceptibility, magnetization, heat capacity, electrical resistivity, and magnetoresistance for magnetic fields applied along both the tetragonal $c$-axis and in the basal $ab$-plane. X-ray diffraction measurements confirm a centrosymmetric, $I4_{1}/amd$ space group of the crystal structure. Despite single-site occupancy of the Gd position in this tetragonal structure, we identify two successive antiferromagnetic phase transitions at Neél temperatures 32~K and 23~K via magnetic susceptibility, heat capacity and transport measurements, as well as a complex magnetic interaction with a magnetic anisotropy that plays an important role in the direction-dependent transport response. Our identification of multiple magnetic phases in Gd$_{2}$AlSi$_{3}$, where Gd is the only magnetic species, helps to elucidate the field-induced skyrmionic behavior in the Gd-based intermetallic compounds.

cond-mat.str-el↗
arXiv2025

Gradual charge order melting in Bi0.5Ca0.5MnO3 induced by ultrahigh magnetic field

We have investigated the magnetic properties of Bi0.5Ca0.5MnO3 under ultrahigh magnetic fields by magnetization measurements. This compound shows the metamagnetic transition which indicates the magnetic field induced charge order melting at the room temperature T = 293 K. We reveled that the temperature dependence of the critical field, where the highest critical field is higher than 100 T. At low temperatures, it has been found that the metamagnetic transitions become broad and vanish in the field ascending process below 70 K. On the other hand, in the field descending process, a clear metamagnetic transition is observed even below 70 K. This unusual behavior can be understood as the gradual charge order melting by magnetic field, and its simultaneous reformation. A coexistence of multiple order parameters can account for the observed characteristic dynamics of the first order phase transition. Finally, we constructed the B-T phase diagram with the unusual critical feature at ultrahigh magnetic fields.

cond-mat.str-el↗
arXiv2025

XRD study of the magnetization plateau above 40 T in the frustrated helimagnet CuGaCr$_{4}$S$_{8}$

CuGaCr$_{4}$S$_{8}$, which contains a chromium breathing pyrochlore network, exhibits diverse magnetic phases, including an incommensurate helical state below 31 K and a 1/2-magnetization plateau above 40 T, owing to the interplay between magnetic frustration and spin-lattice coupling. Here, we perform a single-shot powder x-ray diffraction experiment on CuGaCr$_{4}$S$_{8}$ in a pulsed high magnetic field of 55 T, revealing an orthorhombic-to-cubic (or pseudocubic) structural transition upon entering the 1/2-magnetization plateau phase at low temperatures. This observation suggests the emergence of a commensurate ferrimagnetic order, where a 3-up-1-down spin configuration is realized in each small tetrahedron, and the all-up or all-down in each large tetrahedron. We propose two types of 16-sublattice magnetic structures, which are degenerate within exchange interactions between the first, second, and third nearest neighbors.

cond-mat.mtrl-sci↗
arXiv2024

Pressure evolution of the normal- and superconducting-state properties of the line-nodal material CaSb$_2$ revealed by $^{123}$Sb nuclear quadrupole resonance

CaSb$_2$ is the Dirac line-nodal material that exhibits a superconducting (SC) transition at 1.7 K. In spite of its conventional SC state at ambient pressure, the transition temperature $T_{\mathrm{c}}$ shows a peak structure against hydrostatic pressure. We performed ac magnetic susceptibility and $^{123}$Sb nuclear quadrupole resonance (NQR) measurements on single-crystalline CaSb$_2$ under pressures up to 2.08 GPa. $T_{\mathrm{c}}$ monotonically increased in this pressure region, which is consistent with a previous study. We observed continuous broadening of the NQR spectrum against pressure, which is a sign of unique compression behavior of the lattice. In the normal state, the nuclear spin-lattice relaxation rate 1/$T_1$ is proportional to temperature in all pressure values; typical of a metal. However, 1/$T_1T$ in the normal state is independent of pressure, indicating that the density of states at the Fermi energy $N(E_{\mathrm{F}})$, which is one of the parameters governing $T_{\mathrm{c}}$, is insensitive to pressure. From these results, we conclude that $N(E_{\mathrm{F}})$ does not govern the origin of the enhancement in $T_{\mathrm{c}}$. This is unusual for a weak electron-phonon coupling superconductor. In the SC state, we revealed that the SC gap becomes larger and more isotropic under pressure.

cond-mat.supr-con↗
arXiv2023

Breathing pyrochlore magnet CuGaCr$_{4}$S$_{8}$: Magnetic, thermodynamic, and dielectric properties

We investigate the crystallographic and magnetic properties of a chromium-based thiospinel CuGaCr$_{4}$S$_{8}$. From a synchrotron x-ray diffraction experiment and structural refinement, Cu and Ga atoms are found to occupy the tetrahedral $A$-sites in an alternate way, yielding breathing pyrochlore Cr network. CuGaCr$_{4}$S$_{8}$ undergoes a magnetic transition associated with a structural distortion at 31 K in zero magnetic field, indicating that the spin-lattice coupling is responsible for relieving the geometrical frustration. When applying a pulsed high magnetic field, a sharp metamagnetic transition takes place at 40 T, followed by a 1/2-magnetization plateau up to 103 T. These phase transitions accompany dielectric anomalies, suggesting the presence of helical spin correlations in low-field phases. The density-functional-theory calculation reveals that CuGaCr$_{4}$S$_{8}$ is dominated by antiferromagnetic and ferromagnetic exchange couplings within small and large tetrahedra, respectively, in analogy with CuInCr$_{4}$S$_{8}$. We argue that $A$-site-ordered Cr thiospinels serve as an excellent platform to explore diverse magnetic phases along with pronounced magnetoelastic and magnetodielectric responses.

cond-mat.mtrl-sci↗
arXiv2023

Signatures of a magnetic superstructure phase induced by ultrahigh magnetic fields in a breathing pyrochlore antiferromagnet

The mutual coupling of spin and lattice degrees of freedom is ubiquitous in magnetic materials and potentially creates exotic magnetic states in response to the external magnetic field. Particularly, geometrically frustrated magnets serve as a fertile playground for realizing magnetic superstructure phases. Here, we observe an unconventional two-step magnetostructural transition prior to a half-magnetization plateau in a breathing pyrochlore chromium spinel by means of state-of-the-art magnetization and magnetostriction measurements in ultrahigh magnetic fields available up to 600 T. Considering a microscopic magnetoelastic theory, the intermediate-field phase can be assigned to a magnetic superstructure with a three-dimensional periodic array of 3-up-1-down and canted 2-up-2-down spin molecules. We attribute the emergence of the magnetic superstructure to a unique combination of the strong spin-lattice coupling and large breathing anisotropy.

cond-mat.mtrl-sci↗
arXiv2023

Unveiling new quantum phases in the Shastry-Sutherland compound SrCu2(BO3)2up to the saturation magnetic field

Under magnetic fields, quantum magnets often undergo exotic phase transitions with various kinds of order. The discovery of a sequence of fractional magnetization plateaus in the Shastry-Sutherland compound SrCu2(BO3)2 has played a central role in the high-field research on quantum materials, but so far this system could only be probed up to half the saturation value of the magnetization. Here, we report the first experimental and theoretical investigation of this compound up to the saturation magnetic field of 140 T and beyond. Using ultrasound and magnetostriction techniques combined with extensive tensor-network calculations (iPEPS), several spin-supersolid phases are revealed between the 1/2 plateau and saturation (1/1 plateau). Quite remarkably, the sound velocity of the 1/2 plateau exhibits a drastic decrease of -50%, related to the tetragonal-to-orthorhombic instability of the checkerboard-type magnon crystal. The unveiled nature of this paradigmatic quantum system is a new milestone for exploring exotic quantum states of matter emerging in extreme conditions.

cond-mat.str-el↗
arXiv2023

Complex magnetic phase diagram with a small phase pocket in a three-dimensional frustrated magnet CuInCr$_{4}$S$_{8}$

Frustrated magnets with a strong spin-lattice coupling can show rich magnetic phases and the associated fascinating phenomena. A promising platform is the breathing pyrochlore magnet CuInCr$_{4}$S$_{8}$ with localized $S=3/2$ Cr$^{3+}$ ions, which is proposed to be effectively viewed as an $S=6$ Heisenberg antiferromagnet on the face-centered-cubic lattice. Here, we unveil that CuInCr$_{4}$S$_{8}$ exhibits a complex magnetic phase diagram with a small phase pocket ($A$ phase) by means of magnetization, magnetostriction, magnetocapacitance, and magnetocaloric-effect measurements in pulsed high magnetic fields of up to 60 T. Remarkably, the appearance of $A$ phase is accompanied by anomalous magnetostrictive and magnetocapacitive responses, suggesting the emergence of helimagnetism in contrast to the neighboring commensurate magnetic phases. Besides, the high-entropy nature is confirmed in the high-temperature side of $A$ phase. These features are potentially related to a thermal fluctuation-driven multiple-$q$ state caused by the magnetic frustration, which has been theoretically predicted but yet experimentally undiscovered.

cond-mat.str-el↗
arXiv2022

Enhancement of giant magnetoelectric effect in Ni-doped CaBaCo$_{4}$O$_{7}$

The polar magnet CaBaCo$_{4}$O$_{7}$ is known to exhibit the largest magnetic-field-driven electric polarization change ($ΔP$) associated with an antiferromagnetic (AFM)-ferrimagnetic (FIM) transition in a narrow temperature range between 62 and 69 K. In this work, we investigate the effect of Ni doping on its multiferroic properties, by means of magnetization, electric polarization, dielectric constant, and magnetostriction measurements on single crystals of CaBaCo$_{3.9}$Ni$_{0.1}$O$_{7}$ up to 50 T. In the doped material, two kinds of AFM phases appear below 78 K, accompanying negative $ΔP$. Upon the application of a magnetic field along any crystallographic axis, giant positive $ΔP$ of up to $11 \sim 12$ mC/m$^{2}$ is observed along with an AFM-FIM transition in the whole temperature range below 78 K. The giant magnetoelectric effect inherent in CaBaCo$_{4}$O$_{7}$ can be further enhanced just by a small amount of chemical substitution, in terms of (i) increasing the magnitude of $ΔP$ and (ii) expanding the temperature range in which giant $ΔP$ appears.

cond-mat.mtrl-sci↗
arXiv2021

Charge-changing cross sections for $^{42\textrm{--}51}$Ca and effect of charged-particle evaporation induced by neutron removal reaction

Charge-changing cross sections $σ_\mathrm{CC}$ for $^{42\textrm{--}51}$Ca on a carbon target at around 280~MeV/nucleon have been measured. The measured $σ_\mathrm{CC}$ values differ significantly from the previously developed calculations based on the Glauber model. However, through introduction of the charged-particle evaporation effect induced by the neutron-removal reaction in addition to the Glauber-model calculation, experimental $σ_\mathrm{CC}$ values on $^{12}$C at around 300~MeV/nucleon for nuclides from C to Fe isotopes are all reproduced with approximately 1\% accuracy. This proposed model systematically reproduces $σ_\mathrm{CC}$ data without phenomenological corrections, and can also explain experimental $σ_\mathrm{CC}$ values obtained in other energy regions.

nucl-ex↗
arXiv2021

Physical properties of liquid oxygen under ultrahigh magnetic fields

We studied the acoustic properties of liquid oxygen up to 90 T by means of ultrasound measurements. We observed a monotonic decrease of the sound velocity and an asymptotic increase of the sound attenuation when applying magnetic fields. The unusual attenuation, twenty times as large as the zero-field value, suggests strong fluctuations of the local molecular arrangement. We point out that the observed fluctuations are related to a liquid-liquid transition or crossover, from a small-magnetization to a large-magnetization liquid, which is characterized by a local-structure rearrangement. To investigate higher-field properties of liquid oxygen, we performed single-turn-coil experiments up to 180 T by means of the acoustic, dilatometric, magnetic, and optical techniques. We observed only monotonic changes of these properties, reflecting the absence of the proposed liquid-liquid transition in our experimental conditions.

cond-mat.soft↗
arXiv2021

Higher magnetic-field generation by a mass-loaded single-turn coil

Single-turn coil (STC) technique is a convenient way to generate ultrahigh magnetic fields of more than 100 T. During the field generation, the STC explosively destructs outward due to the Maxwell stress and Joule heating. Unfortunately, the STC does not work at its full potential because it has already expanded when the maximum magnetic field is reached. Here, we propose an easy way to delay the expansion and increase the maximum field by using a mass-loaded STC. By loading clay on the STC, the field profile drastically changes, and the maximum field increases by 4 %. This method offers an access to higher magnetic fields for physical property measurements.

cond-mat.mtrl-sci↗
arXiv2021

Field-induced valence fluctuation in YbB$_{12}$

We performed high-magnetic-field ultrasonic experiments on YbB$_{12}$ up to 59 T to investigate the valence fluctuations in Yb ions. In zero field, the longitudinal elastic constant $C_{11}$, the transverse elastic constants $C_{44}$ and $\left( C_{11} - C_{12} \right)/2$, and the bulk modulus $C_\mathrm{B}$ show a hardening with a change of curvature at around 35 K indicating a small contribution of valence fluctuations to the elastic constants. When high magnetic fields are applied at low temperatures, $C_\mathrm{B}$ exhibits a softening above a field-induced insulator-metal transition signaling field-induced valence fluctuations. Furthermore, at elevated temperatures, the field-induced softening of $C_\mathrm{B}$ takes place at even lower fields and $C_\mathrm{B}$ decreases continuously with field. Our analysis using the multipole susceptibility based on a two-band model reveals that the softening of $C_\mathrm{B}$ originates from the enhancement of multipole-strain interaction in addition to the decrease of the insulator energy gap. This analysis indicates that field-induced valence fluctuations of Yb cause the instability of the bulk modulus $C_\mathrm{B}$.

cond-mat.str-el↗
arXiv2021

Particle-hole symmetry breaking in a spin-dimer system TlCuCl$_3$ observed at 100 T

The entire magnetization process of TlCuCl$_3$ has been experimentally investigated up to 100 T employing the single-turn technique. The upper critical field $H_{c2}$ is observed to be 86.1 T at 2 K. A convex slope of the $M$-$H$ curve between the lower and upper critical fields ($H_{c1}$ and $H_{c2}$) is clearly observed, which indicates that a particle-hole symmetry is broken in TlCuCl$_3$. By quantum Monte Carlo simulation and the bond-operator theory method, we find that the particle-hole symmetry breaking results from strong inter-dimer interactions.

cond-mat.str-el↗
arXiv2019

Swelling of doubly magic $^{48}$Ca core in Ca isotopes beyond $N=28$

Interaction cross sections for $^{42\textrm{-}51}$Ca on a carbon target at 280 MeV/nucleon have been measured for the first time. The neutron number dependence of derived root-mean-square matter radii shows a significant increase beyond the neutron magic number $N=28$. Furthermore, this enhancement of matter radii is much larger than that of the previously measured charge radii, indicating a novel growth in neutron skin thickness. A simple examination based on the Fermi-type distribution, and the Mean-Field calculations point out that this anomalous enhancement of the nuclear size beyond $N=28$ results from an enlargement of the core by a sudden increase in the surface diffuseness of the neutron density distribution, which implies the swelling of the bare $^{48}$Ca core in Ca isotopes beyond $N=28$.

nucl-ex↗
arXiv2014

Charmonium spectra and dispersion relation with improved Bayesian analysis in lattice QCD

We study the charmonium spectral functions at finite momentum and the dispersion relation of $η_c$ at finite temperature. For the analysis of the spectral function, we use an extended maximum entropy method (MEM). We perform the MEM analysis for the product space of Euclidean correlators in different channels or momenta to incorporate information encoded in correlations among the Euclidean correlators in MEM. We find that this method can improve the error of the reconstructed spectral images. To study the dispersion relation, we introduce a definition of the peak position in the spectral image in which the associated error can be estimated on the basis of MEM. We find that the dispersion relation of $η_c$ at finite temperature follows the Lorentz invariant form even near the dissociation temperature $T\simeq1.7T_c$.

hep-lat↗