Satoshi Tsutsui

The Mixed Valence States in the Unconventional Heavy Fermion Compound SmOs4Sb12

The X-ray absorption spectra of the heavy fermion compounds SmFe 4 P 12 and SmOs 4 Sb 12 have been measured near the Sm L 3 -edge at selected temperatures below 300 K. The spectra show the valence of Sm ions in SmFe 4 P 12 to be trivalent between 14 and 300 K with no significant temperature dependence. In contrast, that in SmOs 4 Sb 12 is 2.83 at 300 K and shows a significant decrease below 150 K, indicating an important role of the nonmagnetic Sm 2+ ions in the heavy fermion state that are insensitive to an applied magnetic field.

Kohn anomaly in MgB2 by inelastic X-ray scattering.

We study phonons in MgB2 using inelastic x-ray scattering (1.6 and 6 meV resolution). We clearly observe the softening and broadening of the crucial E(2g) mode through the Kohn anomaly along GammaM, in excellent agreement with ab initio calculations. Low temperature measurements (just above and below T(c)) show negligible changes for the momentum transfers investigated and no change in the E(2g) mode at A between room temperature and 16 K. We report the presence of a longitudinal mode along GammaA near in energy to the E(2g) mode that is not predicted by theory.

A Possible Novel Magnetic Ordering in SmRu4P12

We have carried out X-ray absorption spectroscopy, 149 Sm nuclear resonant forward scattering, and 99 Ru Mossbauer spectroscopy of SmRu 4 P 12 . The X-ray absorption spectra indicate that the Sm ions are trivalent up to 14 K. The quantum beats due to magnetic dipolar ordering are observed at 4.5 K in 149 Sm nuclear resonant forward scattering. The temperature dependence of time-integrated intensity in 149 Sm nuclear forward scattering suggests that the magnetic dipolar ordering occurs just below the metal–insulator transition temperature. No significant changes in the parameters are observed between 77 and 5 K in 99 Ru Mossbauer spectroscopy. The present result suggests a magnetic ordering accompanied by a magnetic dipole moment at the metal–insulator transition temperature in SmRu 4 P 12 in spite of the proposal of the magnetic ordering accompanied by a T β -type octupole.

Softening of Cu-O bond stretching phonons in tetragonal HgBa2CuO4+delta.

Phonons in nearly optimally doped HgBa(2)CuO(4+delta) were studied by inelastic x-ray scattering. The dispersion of the low-energy modes is well described by a shell model, while the Cu-O bond stretching mode at high energy shows strong softening towards the zone boundary, which deviates strongly from the model. This seems to be common in the hole-doped high-T(c) superconducting cuprates, and, based on this work, not related to a lattice distortion specific to each material.

Liquid iron‐sulfur alloys at outer core conditions by first‐principles calculations

We examined the density, bulk sound (compressional) velocity, and Gruneisen parameter of liquid pure Fe, Fe100H28 (0.50 wt % H), Fe88H40 (0.81 wt % H), and Fe76H52 (1.22 wt % H) at Earths outer core pressure and temperature (P-T) conditions (~100 to 350 GPa, 4000 to 7000 K) based on first-principles molecular dynamics calculations. The results demonstrate that the thermodynamic Gruneisen parameter of liquid iron alloy decreases with increasing pressure, temperature, and hydrogen concentration, indicating a relatively small temperature gradient in the outer core when hydrogen is present. Along such temperature profile, both the density and compressional velocity of liquid iron containing ~1 wt % hydrogen match seismological observations. It suggests that hydrogen could be a primary light element in the core, although the shear velocity of the inner core is not reconciled with solid Fe-H alloy and thus requires another impurity element.

Transverse excitations in liquid Sn

Transverse acoustic (TA) excitation modes were observed in inelastic x-ray scattering (IXS) spectra of liquid Sn. The excitation energies and widths of the TA modes are in good agreement with results of an ab initio molecular dynamics simulation. By comparing current correlation spectra between the experimental and theoretical results quantitatively, we have concluded that the TA modes can be detected experimentally through the quasi-TA branches in the longitudinal current correlation spectra. The lifetime and propagation length of the TA modes were determined to be ~0.7 ps and 0.8-1.0 nm, respectively, corresponding to the size of cages formed instantaneously in liquid Sn.

Lattice Dynamics of LaFeAsO1-xFx and PrFeAsO1-y via Inelastic X-Ray Scattering and First-Principles Calculation

The lattice dynamics of LaFeAsO 1- x F x ( x =0,0.1) and PrFeAsO 1- y ( y ∼0.1) are investigated using inelastic x-ray scattering and ab-initio calculation. Measurements of powder samples provide an approximation to the phonon DOS, while dispersion is measured from a single crystal of PrFeAsO 1- y . A model that agrees reasonably well with all of the data at room temperature is built from results of ab-initio calculations by reducing the strength of the Fe–As bond by 30%.The lattice dynamics of LaFeAsO 1- x F x ( x =0,0.1) and PrFeAsO 1- y ( y ∼0.1) are investigated using inelastic x-ray scattering and ab-initio calculation. Measurements of powder samples provide an approximation to the phonon DOS, while dispersion is measured from a single crystal of PrFeAsO 1- y . A model that agrees reasonably well with all of the data at room temperature is built from results of ab-initio calculations by reducing the strength of the Fe–As bond by 30%.

Carbon-depleted outer core revealed by sound velocity measurements of liquid iron–carbon alloy

The relative abundance of light elements in the Earths core has long been controversial. Recently, the presence of carbon in the core has been emphasized, because the density and sound velocities of the inner core may be consistent with solid Fe7C3. Here we report the longitudinal wave velocity of liquid Fe84C16 up to 70 GPa based on inelastic X-ray scattering measurements. We find the velocity to be substantially slower than that of solid iron and Fe3C and to be faster than that of liquid iron. The thermodynamic equation of state for liquid Fe84C16 is also obtained from the velocity data combined with previous density measurements at 1 bar. The longitudinal velocity of the outer core, about 4% faster than that of liquid iron, is consistent with the presence of 4–5 at.% carbon. However, that amount of carbon is too small to account for the outer core density deficit, suggesting that carbon cannot be a predominant light element in the core.

Transverse excitations in liquid Fe, Cu and Zn

Transverse acoustic (TA) excitation modes were observed in inelastic x-ray scattering spectra of liquid Fe, Cu and Zn. From the analysis of current correlation functions, we concluded that TA excitation modes can experimentally be detected through the quasi-TA branches in the longitudinal current correlation spectra in these liquid metals. The microscopic elastic constants are estimated and a characteristic difference from macroscopic polycrystalline value was found in Poissons ratio of liquid Fe, which shows an extremely softer value of ∼0.38 compared with the macroscopic value of ∼0.275. The lifetime of the TA modes were determined to be ∼0.45 ps for liquid Fe and Cu and ∼0.55 ps for liquid Zn, reflecting different interatomic correlations between liquid transition metals and non-transition metals. The propagation length of the TA modes are ∼0.85 nm in all of liquid metals, corresponding to the size of icosahedral or similar size of cages formed instantaneously in these liquid metals.

Precise determination of elastic constants by high-resolution inelastic X-ray scattering.

Inelastic X-ray scattering (IXS) measurements have been performed on an MgO single crystal in order to evaluate IXS as a methodology for accurate and precise determination of elastic constants and sound velocities. By performing the IXS experiment using a 12-analyzer array, the complete set of single-crystal elastic constants of MgO were determined to a precision better than 0.8% (sound velocities to better than 0.2%). The results are consistent with values in the literature. The precision and accuracy of this work, which is significantly better than other published work to date, demonstrates the potential of IXS in determining elastic properties.