arXiv subjects

M. Mizumaki

Publications and source records attributed to M. Mizumaki.

11 recordsLinked to original sources

arXiv2024

Field-Induced Criticality in YbCu4Au

YbCu4Au is a unique material exhibiting multiple quantum fluctuations simultaneously. In this study, we investigated the field-induced criticality in YbCu4Au, based on comprehensive micro and macro measurements, including powder X-ray diffraction (XRD), neutron powder diffraction (NPD), nuclear magnetic resonance, magnetization, resistivity, specific heat, muon spin rotation relaxation (muSR), and X-ray absorption spectroscopy (XAS). Single crystals of YbCu4Au were grown, and their crystal structure was determined using XRD, and NPD measurements. Magnetic successive transitions were observed below 1 T by specific heat, resistivity, NPD, and muSR measurements. XAS measurements further indicate that the valence of Yb ions (+2.93) remained unchanged above 2 T. Moreover, the change in quadrupole frequency observed in the previous study is attributable to the electric quadrupole, as the expected value of the electric quadrupole was finite under magnetic fields [S. Wada et al., Journal of Physics: Condensed Matter, 20, 175201 (2008).]. These experimental results suggest that YbCu4Au exhibited bicritical behavior near 1 T, arising from the competition between RKKY interaction, accounting for the magnetic phases, and the Zeeman effect.

cond-mat.str-el↗

arXiv2023

Efficient NMR measurement and data analysis supported by the Bayesian inference : The case of the heavy fermion compound YbCo2Zn20

We propose a data-driven technique to infer microscopic physical quantities from nuclear magnetic resonance(NMR) spectra, in which the data size and quality required for the Bayesian inference are investigated. The $^{59}$Co-NMR measurement of YbCo$_2$Zn$_{20}$ single crystal generates complex spectra with 28 peaks. By exploiting the site symmetry in the crystal structure, the isotropic Knight shift $K_{iso}$ and nuclear quadrupole resonance(NQR) frequency $ν_Q$ were estimated to be $K_{iso} = 0.7822 \pm 0.0090 \%$, $ν_Q = 2.008 \pm 0.016$ MHz ( T = 20 K, H $\simeq$ 10.2 T) by analyzing only 30 data points from one spectrum. The estimation of $ν_Q$ is consistent with the precise value obtained in the NQR experiment. Our method can significantly reduce the measurement time and the computational cost of data analysis in NMR experiments.

cond-mat.mtrl-sci↗

arXiv2022

Compressed Sensing of Compton Profiles for Fermi Surface Reconstruction: Concept and Implementation

Compton scattering is a well-established technique that can provide detailed information about electronic states in solids. Making use of the principle of tomography, it is possible to determine the Fermi surface from sets of Compton-scattering data with different scattering axes. Practical applications, however, are limited due to long acquisition time required for measuring along enough number of scattering directions. Here, we propose to overcome this difficulty using compressed sensing. Taking advantage of a hidden sparsity in the momentum distribution, we are able to reconstruct the three-dimensional momentum distribution of bcc-Li, and identify the Fermi surface with as little as 14 directions of scattering data with unprecedented accuracy. This compressed-sensing approach will permit further wider applications of the Compton scattering experiments.

cond-mat.mtrl-sci↗

arXiv2020

Isotropic parallel antiferromagnetism in the magnetic-field-induced charge-ordered state of SmRu$_4$P$_{12}$ caused by $p$-$f$ hybridization

Nature of the field-induced charge ordered phase (phase II) of SmRu$_4$P$_{12}$ has been investigated by resonant x-ray diffraction (RXD) and polarized neutron diffraction (PND), focusing on the relationship between the atomic displacements and the antiferromagnetic (AFM) moments of Sm. From the analysis of the interference between the non-resonant Thomson scattering and the resonant magnetic scattering, combined with the spectral function obtained from x-ray magnetic circular dichroism, it is shown that the AFM moment of Sm prefers to be parallel to the field ($m_{\text{AF}} \parallel H$), giving rise to large and small moment sites around which the P$_{12}$ and Ru cage contract and expand, respectively. This is associated with the formation of the staggered ordering of the $Γ_7$-like and $Γ_8$-like crystal-field states, providing a strong piece of evidence for the charge order. PND was also performed to obtain complementary and unambiguous conclusion. In addition, isotropic and continuous nature of the phase II is demonstrated by the field-direction invariance of the interference spectrum in RXD. Crucial role of the $p$-$f$ hybridization is shown by resonant soft x-ray diffraction at the P $K$-edge ($1s\leftrightarrow 3p$), where we detected a resonance due to the spin polarized $3p$ orbitals reflecting the AFM order of Sm.

cond-mat.str-el↗

arXiv2018

Novel Kondo-like behavior near magnetic instability in SmB$_6$ : temperature and pressure dependences of Sm valence

We report a systematic study of Sm valence in the prototypical intermediate valence compound SmB$_6$. Sm mean valence, $v_{\rm Sm}$, was measured by X-ray absorption spectroscopy as functions of pressure ($1<P<13$ GPa) and temperature ($3<T<300$ K). Pressure induced magnetic order (MO) was detected above $P_c = 10$ GPa by resistivity measurements. A shift toward localized $4f$ state with increasing $P$ and/or $T$ is evident from an increase in $v_{\rm Sm}$. However $v_{\rm Sm}$ at $P_c$ is anomalously far below 3, which differs from the general case of nonmagnetic-magnetic transition in Yb and Ce compounds. From the $T$ dependence of $v_{\rm Sm}(P,T)$, we found that $v_{\rm Sm}(P,T)$ consists of two different characteristic components: one is associated with low-energy electronic correlations involving Kondo like behavior, and the other with high-energy valence fluctuations.

cond-mat.str-el↗

arXiv2015

Pressure-Induced Valence Crossover and Novel Metamagnetic Behavior near the Antiferromagnetic Quantum Phase Transition of YbNi$_{3}$Ga$_{9}$

We report electrical resistivity, ac magnetic susceptibility and X-ray absorption spectroscopy measurements of intermediate valence YbNi$_{3}$Ga$_{9}$ under pressure and magnetic field. We have revealed a characteristic pressure-induced Yb valence crossover within the temperature-pressure phase diagram, and a first-order metamagnetic transition is found below $P_{\rm c}$ $\sim$ 9 GPa where the system undergoes a pressure-induced antiferromagnetic transition. As a possible origin of the metamagnetic behavior, a critical valence fluctuation emerging near the critical point of the first-order valence transition is discussed on the basis of the temperature-field-pressure phase diagram.

cond-mat.str-el↗

arXiv2013

Insulator-to-Superconductor Transition upon Electron Doping in a BiS$_{2}$-Based Superconductor Sr$_{1-x}$La$_{x}$FBiS$_{2}$

Effects of electron doping on the BiS$_2$-based superconductors Sr$_{1-x}$La$_x$FBiS$_2$ ($0\le x\le 0.6$) have been investigated using the systematically synthesized polycrystals. The pristine compound is a band insulator with the BiS$_2$ layer, which accommodates electron carriers through the La substitution for Sr, as evidenced by the change in x-ray absorption spectra reflecting the occupancy of Bi 6$p$ orbitals. With increasing the carrier density, the resistivity progressively decreases and a bad metallic state appears for $x\ge0.45$, where bulk superconductivity manifests itself below approximately 3 K. The value of $T_{\rm c}$ gradually increases with decreasing $x$ from 0.6 to 0.45 and immediately decreases down to zero at the critical concentration of $x\sim 0.4$, resulting in an insulator-superconductor transition highly sensitive to the carrier density. Thermodynamic measurements furthermore have revealed the possible enhancement of the superconducting coupling strength as the insulating phase is approached. The obtained superconducting phase diagram is markedly different from the broad dome-shaped superconducting phase previously reported for $R$O$_{1-x}$F$_x$BiS$_2$ ($R$: rare-earth ion), suggesting a strong influence of the blocking layer on the superconductivity. Instead all these features are similar to those observed in Li-intercalated ZrNCl superconductor, except for the critical electron concentration of as low as 6% in the latter compound. For the present superconductor, notably, the existence of hole-type carriers has been indicated in the normal state from the Hall effect measurements. The Sr$_{1-x}$La$_x$FBiS$_2$ system providing the phase diagram for the rigid-band doping in the BiS$_2$ layer would be another prototypical example of superconductivity derived from a doped layered band insulator, hosting both hole-like and electron-like Fermi surfaces.

cond-mat.supr-con↗

arXiv2013

Synchrotron X-ray Spectroscopy Study on the Valence State in alpha- and beta-YbAlB4 at Low Temperatures and High Magnetic Fields

The valence state of Yb ions in beta-YbAlB4 and its polymorph alpha-YbAlB4 has been investigated by using X-ray absorption and emission spectroscopy in SPring-8 at temperatures from 2 to 280 K. The observed Yb valence is 2.78 +- 0.01 in beta-YbAlB4 at 2 K by using the X-ray emission spectroscopy. The valence is found to gradually increase with increasing temperature toward the trivalent state, and the characteristic temperature of the valence fluctuation is expected to be about 290 K. We also found a small increase in the Yb valence (~0.002) by applying a magnetic field of 32 T at 40 K to beta-YbAlB4.

cond-mat.str-el↗

arXiv2011

Pressure-induced changes in the magnetic and valence state of EuFe2As2

We present the results of electrical resistivity, ac specific heat, magnetic susceptibility, X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) of the ternary iron arsenide EuFe2As2 single crystal under pressure. Applying pressure leads to a continuous suppression of the antiferromagnetism associated with Fe moments and the antiferromagnetic transition temperature becomes zero in the vicinity of a critical pressure Pc ~2.5-2.7 GPa. Pressure-induced re-entrant superconductivity, which is highly sensitive to the homogeneity of the pressure, only appears in the narrow pressure region in the vicinity of Pc due to the competition between superconductivity and the antiferromagnetic ordering of Eu2+ moments. The antiferromagnetic state of Eu2+ moments changes to the ferromagnetic state above 6 GPa. We also found that the ferromagnetic order is suppressed with further increasing pressure, which is connected with a valence change of Eu ions.

cond-mat.supr-con↗

arXiv2005

Roles of two successive phase transitions in new spin-Peierls system TiOBr

In this sturdy, we determine the roles of two successive phase transitions in the new spin-Peierls system TiOBr by electron and synchrotron X-ray diffraction analyses. Results show an incommensurate superstructure along the h- and k-directions between Tc1=27K and Tc2=47K, and a twofold superstructure which is related to a spin-Peierls lattice distortion below Tc1. The diffuse scattering observed above Tc2 indicates that a structural correlation develops at a high temperature. We conclude that Tc2 is a second-order lock-in temperature, which is related to the spin-Peierls lattice distortion with the incommensurate structure, and that Tc1 is from incommensurate to commensurate phase transition temperature accompanying the first-order spin-Peierls lattice distortion.

cond-mat.str-el↗

arXiv2004

Relationship between charge stripe order and structural phase transitions in La$_{1.875}$Ba$_{0.125-x}$Sr$_{x}$CuO$_{4}$

The nature of charge stripe order and its relationship with structural phase transitions were studied using synchrotron X-ray diffraction in La$_{1.875}$Ba$_{0.125-x}$Sr$_{x}$CuO$_{4}$ ($0.05\leq x\leq 0.10$). For $x=0.05$, as temperature increased, incommensurate superlattice peaks associated with the charge order disappeared just at the structural phase transition temperature, $T_{\rm d2}$. However, for $x=0.075$ and 0.09, the superlattice peaks still existed as a short range correlation even above $T_{\rm d2}$, indicating a precursor of charge ordering. Furthermore, temperature dependences of the superlattice peak intensity, correlation length, and incommensurability for $x=0.05$ are different from those for $x=0.075$ and 0.09. These results suggest that the transition process into the charge stripe order strongly correlates with the order of the structural phase transitions. A quantitative comparison of the structure factor associated with the charge order have been also made for all the samples.

cond-mat.supr-con↗