arXiv subjects

H. Wada

Publications and source records attributed to H. Wada.

8 recordsLinked to original sources

arXiv2026

The sigma meson ($f_0$) at finite temperature with truncated overlap fermions

We study the temperature dependence of meson screening masses in two-flavour lattice QCD using dynamical truncated overlap fermions (TOF), a type of lattice chiral fermions. The screening masses for the $\pi$, $\rho$, $a_1$, $a_0$, and the sigma $(f_0)$ mesons are extracted by computing spatial correlation functions. Above the pseudocritical temperature $T_{\rm pc}$, the $\pi$ and $f_0$ screening masses become degenerate, consistent with chiral restoration. The $(\pi,f_0)$ and $(\rho,a_1)$ pairs also show the expected degeneracy. Decomposition of the $f_0$ propagator reveals that the connected contribution dominates above $T_{\rm pc}$, while the disconnected part becomes significant below $T_{\rm pc}$, explaining the reduced statistical clarity observed at low $T$. These results demonstrate that dynamical TOF simulations can capture the qualitative thermal behaviour of the scalar sector.

hep-lat↗

arXiv2019

Study of photoinduced valence dynamics in EuNi$_2$(Si$_{0.21}$Ge$_{0.79}$)$_2$ through time-resolved X-ray absorption spectroscopy

The photoinduced valence dynamics of EuNi$_2$(Si$_{0.21}$Ge$_{0.79}$)$_2$ are investigated using time-resolved X-ray absorption spectroscopy for Eu $M_5$-edge. Through the pump-probe technique with synchrotron X-ray and Ti:sapphire laser pulse, a photoinduced valence transition is observed from Eu$^{3+}$ to Eu$^{2+}$. Because the lifetime of a photoinduced state can be up to 3 ns, a metastable state is considered to be realized. By comparing the experimental results with the theoretical calculations, the photoinduced valence transition between Eu 4$f$ and conduction electrons is quantitatively evaluated.

cond-mat.mtrl-sci↗

arXiv2019

Evidence for gradual evolution of low-energy fluctuations underlying the first-order structural and valence order in YbPd

The valence orders at $T_a=125$ K and $T_b=105$ K in the cubic compound YbPd have been investigated by $^{105}$Pd-nuclear magnetic resonance (NMR) measurements. Significant decrease in the density of states at the Fermi energy below $T_a$ is evident from the measurement of nuclear spin lattice relaxation rate $1/T_1$, suggesting that the instabilities of Fermi surface are associated with the transitions. Moreover we observed the unusual evolution of low-energy fluctuations toward the valence transition at $T_a$ behind its drastic first-order nature. The structural transition accompanying the valence order may occur as a result of cooperative effect of Fermi surface and valence instabilities.

cond-mat.str-el↗

arXiv2009

X-ray Magnetic Circular Dichroism of Valence Fluctuating State in Eu at High Magnetic Fields

X-ray magnetic circular dichroism (XMCD) at the Eu L-edge (2p->5d) in two compounds exhibiting valence fluctuation, namely EuNi2(Si0.18Ge0.82)2 and EuNi2P2, has been investigated at pulsed high magnetic fields of up to 40 T. A distinct XMCD peak corresponding to the trivalent state (Eu3+; f6), whose ground state is nonmagnetic (J=0), was observed in addition to the main XMCD peak corresponding to the magnetic (J=7/2) divalent state (Eu2+; f7). This result indicates that the 5d electrons belonging to both valence states are magnetically polarized. It was also found that the ratio P5d(3+)/P5d(2+) between the polarization of 5d electrons (P5d) in the Eu3+ state and that of Eu2+ is ~ 0.1 in EuNi2(Si0.18Ge0.82)2 and ~ 0.3 in EuNi2P2 at magnetic fields where their macroscopic magnetization values are the same. The possible origin of the XMCD of the Eu3+ state and an explanation of the dependence of P5d(3+)/P5d(2+) on the material are discussed in terms of hybridization between the conduction electrons and the f electrons.

cond-mat.str-el↗

arXiv2008

The low-lying Scalar Mesons and Related Topics

After presenting the motivations to explore the low-lying scalar mesons such as the $σ$, $a_0$ and $κ$ in the unquenched as well as quenched lattice QCD, we review the works done by our collaboration (SCALAR Collaboration) with a what-to-do-next list. We briefly mention the imporatance to explore the $N_c$ dependence of and possible effects of the $U_A(1)$ anomaly to the properties the low-lying scalar mesons.

hep-lat↗

arXiv2007

Fabrication of high performance MgB2 wires by an internal Mg diffusion process

We succeeded in the fabrication of high-Jc MgB2/Fe wires applying the internal Mg diffusion (IMD) process with pure Mg core and SiC addition. A pure Mg rod with 2 mm diameter was placed at the center of a Fe tube, and the space between Mg and Fe tube was filled with B powder or the powder mixture of B-(5mol%)SiC. The composite was cold worked into 1.2mm diameter wire and finally heat treated at temperatures above the melting point of Mg(~650oC). During the heat treatment liquid Mg infiltrated into B layer and reacted with B to form MgB2. X-ray diffraction analysis indicated that the major phase in the reacted layer is MgB2. SEM analysis shows that the density of MgB2 layer is higher than that of usual powder-in-tube(PIT) processed wires. The wires with 5mol% SiC addition heat treated at 670oC showed Jc values higher than 105A/cm2 in 8T and 41,000A/cm2 in 10T at 4.2K. These values are much higher than those of usual PIT processed wires even compared to the ones with SiC addition. Higher density of MgB2 layer obtained by the diffusion reaction is the major cause of this excellent Jc values.

cond-mat.supr-con↗

arXiv2005

Temperature dependent Eu 3d-4f X-ray Absorption and Resonant Photoemission Study of the Valence Transition in $EuNi_2(Si_{0.2}Ge_{0.8})_2$

We study the mixed valence transition ($T$$_{v}$ $\sim$80 K) in EuNi$_{2}$(Si$_{0.2}$Ge$_{0.8}$)$_{2}$ using Eu 3$d-4f$ X-ray absorption spectroscopy (XAS) and resonant photoemission spectroscopy (RESPES). The Eu$^{2+}$ and Eu$^{3+}$ main peaks show a giant resonance and the spectral features match very well with atomic multiplet calculations. The spectra show dramatic temperature ($T$)-dependent changes over large energies ($\sim$10 eV) in RESPES and XAS. The observed non-integral mean valencies of $\sim$2.35 $\pm$ 0.03 ($T$ = 120 K) and $\sim$2.70 $\pm$ 0.03 ($T$ = 40 K) indicate homogeneous mixed valence above and below $T$$_{v}$. The redistribution between Eu$^{2+}$$4f^7$+$[spd]^0$ and Eu$^{3+}$$4f^6$+$[spd]^1$ states is attributed to a hybridization change coupled to a Kondo-like volume collapse.

cond-mat.str-el↗

arXiv2001

I=0 scalar channel

Using lattice QCD with dynamical Wilson fermions, we study I=0 and $J^{P}=0^{+}$ channel which is constructed by $\frac{1}{\sqrt{2}}(\bar{u}u+\bar{d}d)|0>$, in order to search for the $σ$ meson. Our preliminary result shows that the connected and disconnected diagrams contribute to the $σ$ meson propagator in the same order.

hep-lat↗