Through a high-precision soft x-ray magnetic circular dichroism (XMCD) study of the intermediate-valence compound SmOs4Sb12, we show our successful approach of revealing unprecedented details of Kondo screening below a characteristic temperature of T-0 similar to 20 K in the paramagnetic phase. The multiplet XMCD structure at the Sm M-5 edge sensitive to the 4f configuration enabled us to observe a clear difference between the temperature evolution above and below T-0 with one- and two-component behavior, respectively. Our findings are in strong contrast to the conventional Kondo crossover that coincides with the valence transition, but are qualitatively accounted for by theoretical XMCD predictions combined with the two-fluid phenomenology recently proposed. This work contributes to the large context of Kondo physics that is closely related to quantum criticality in heavy fermion systems.

The n-/p-type stability of a silicon clathrate in which silicon was substituted with nickel or platinum was evaluated by density functional theory calculations. Then, Ba8Pt5Si41 and Ba8Pt1.5Ni3.5Si41 were synthesized, and their thermoelectric properties were investigated. The polycrystalline compounds, which have a type-I clathrate structure, were prepared through arc melting and spark-plasma-sintering. The crystal structures and elemental compositions of the synthesized samples were characterized via powder x-ray diffraction and electron microprobe analyses, respectively. The temperature dependence of both the electrical resistivity and the Seebeck coefficient was measured.

Thermoelectric materials suitable for practical thermoelectric power generators should, ideally, be based on light elements, for example Si and Al, which are abundantly available. For this reason, silicon clathrate compounds in which both Ga and Al were substituted for Si were synthesized and their thermoelectric properties were investigated. The temperature-dependent electrical resistivity of the samples indicated their metallic nature, and their negative Seebeck coefficient suggested that charge transport in the samples was mainly through electron transport. The maximum absolute value of the Seebeck coefficient achieved was −180 μV/K at 1040 K for Ba7.90Ga13.8Al2.29Si30.0. Thus, these materials have potential for use in practical thermoelectric power generators.

A characteristic behavior called rattling has been observed in several filled skutterudites RT4X12 (R: rare earth, T: transition metal, X: pnictogen) by various methods. However, rattling phenomena have not been systematically understood because the characteristics of rattling are different when observed with different measurement methods. We have systematically investigated rattling using X-ray absorption fine structure (XAFS) analysis in order to gain a unified picture of rattling phenomena in filled skutterudites. The temperature dependence of extended X-ray absorption fine structure (EXAFS) thermal factors provides both dynamic and static information. Off-center distances were derived from the static distortions obtained by Einstein-model fitting to the EXAFS Debye–Waller factors. The key relation between the off-center distance, defined by the interatomic distance between the rare-earth and pnictogen, and the cage space, defined by the atomic and ionic radii of the rare-earth and pnictogen, was shown. The off-center distance was found to be approximately proportional to the cage space in the large cage systems (R–T–X combinations). The rattling effect depends upon not only the existence of a potential barrier in the interatomic potentials between the rare-earth ions and pnictogen atoms but also the coherence in the motion of rare-earth ions.

We have investigated the electrical resistivity rho and Hall resistivity rho(H) of the filled skutterudite PrFe4P12 as functions of both temperature T down to 30 mK and magnetic field H up to 17.9 T for the field directions near the [111] axis. At low temperatures, we observed a clear anomaly in rho(H) and rho(H) within a limited range of field directions close to H parallel to [111] at around 8 T, reflecting the onset of the high-field ordered phase (HOP) reported previously. rho exhibits a crater like structure as a function of the field direction in the ((1) over bar 10) plane with a minimum near the [111] axis. Magnetoresistance exhibits clear anomalies across the boundaries of both the low-field scalar-order phase (SOP) and the HOP. With decreasing temperature, the phase boundaries of the high-field side of the SOP and the low-field side of the HOP approach more slowly than was inferred previously. The carrier density in the HOP evaluated by the rho and rho(H) measurements is more than an order of magnitude higher than that in the SOP, which rules out q = (0, 0, 1) as the ordering wave vector for the HOP. Within the HOP, we found an additional anomaly accompanied by a clear hysteresis at around 17 T below similar to 0.75 K, indicating the existence of a new phase boundary. The existence of the additional state in the HOP may indicate that almost-degenerate multiple internal degrees of freedom are involved in the HOP. This finding should provide an important clue to clarify the nature and origin of the HOP.

Extended x-ray absorption fine structure (EXAFS) measurements were carried out at the K-edge of rare-earth ions in REFe4P12 (RE = La, Ce, Pr, Nd, and Sm) at various temperatures. Distance between a rare-earth atom and neighboring atoms in each REFe4P12 compound was determined in this work. The obtained results agree reasonably with previous results of diffraction experiments. The temperature dependence of EXAFS amplitude was successfully analyzed using the Einstein model in each compound. The Einstein temperatures obtained by the analyses show a significant rare-earth dependence. Quantitative comparison between the present EXAFS measurements and phonon measurements such as inelastic x-ray/neutron scattering suggests that reduced mass treatment is essential for estimating Einstein temperatures. This indicates that finite binding energy exists between a rare-earth atom and P atoms at least in REFe4P12 compounds.

Heat capacity and ac-susceptibility measurements under high pressure are carried out in SmOs4Sb12. Application of pressure increases the Curie temperature T-C and enhances the heat-capacity jump at T-C. On the other hand, the peak value of ac-susceptibility at T-C decreases above 1 GPa and then almost vanishes at 3.6 GPa. These experimental facts suggest that the ordered state in SmOs4Sb12 is not simple ferromagnetic state but possibly multipolar ordered state.

We carried out X-ray absorption spectroscopy, powder diffraction experiment using synchrotron radiation and inelastic X-ray scattering to elucidate Sm atomic and charge dynamics in SmOs4Sb12. The X-ray absorption spectra demonstrate that SmOs4Sb12 is a Sm valence fluctuation compound. The inelastic Xray scattering and powder diffraction experiments demonstrate the presence of the anharmonic Sm modes with low energy. We discussed here the correlation between the low-lying Sm modes and Sm valence fluctuation in SmOs4Sb12.

Analysis of previously published data of electrical resistivity and specific heat in SmOs4Sb12 has been made combining with other physical quantities. The results demonstrate that the heavy-fermion state develops gradually in the temperature range of 10 - 100 K with decreasing temperature and to attain the Fermi-liquid characteristics below similar to 2 K. In the same temperature (energy) range of 10 - 100 K, anomalies appear in several quantities corresponding to the rattling anharmonic ion oscillations and unidentified charge fluctuations, suggesting that such electric charge degrees of freedom are deeply involved in the heavy quasiparticle formation. We discuss a possible scenario in which those electric charge degrees of freedom are deeply involved in the heavy quasiparticle formation, whereby the "magnetic-field insensitive" feature is acquired.

An antiferromagnetic (AFM) ground state and a possible high-field ordered state in magnetic fields H >1 T of a filled-skutterudite compound CeOs4Sb12 were investigated by the muon spin rotation and relaxation method. In a zero applied field, a spontaneous local field due to the weak AFM ordering was observed below similar to 1.6 K. The magnetic volume fraction gradually increases below 1.6 K with decreasing temperature, suggesting that this phase is sensitive to sample quality. The magnitude of the ordered dipole moment in the AFM state was estimated to be in the range of 0.11-0.17 mu(B)/Ce at 0.1 K. In a field of 2 T applied along the [001] direction, clear anomalies in the muon Knight shift and linewidth were observed at similar to 1.5 K, consistent with the phase-transition scenario into the high-field ordered state suggested from specific-heat, resistivity, elastic, and NMR anomalies. The possibility of multipole ordering in the high-field phase was discussed.

The order parameter in the pressure-induced insulating phase of the filled skutterudite compound PrFe4P12 has been investigated using a high-pressure single-crystal neutron diffraction technique. Clear evidence of the antiferromagnetic order with the propagation vector q = (1, 0, 0) was observed in the insulating phase above 2.7 GPa. The q = (1, 0, 0) structure is identical with that in the nonmagnetic ordered phase below 2.5 GPa and with the nesting property of the Fermi surface. The observed magnetic moment of the Pr ion is 2 mu(B) and almost pressure-independent up to at least 4.2 GPa. The 2 mu(B) magnetic moment originates from the dipole in the low-lying quasi-quartet crystal field state. The pressure-induced antiferromagnetic structure at 3.2 GPa is suppressed by applying a magnetic field of about 1.5 T, which is interpreted as a flop of magnetic moments into the alignment of the ferromagnetic state. This brings about a steep decrease in the electrical resistivity due to the disappearance of the antiferromagnetic superstructure.

By specific heat measurements on Pr(Os1−xRux)4Sb12, we have studied the x-dependences of the 4f-electron crystalline-electric-field first excitation energy and the rattling energy of the Pr ion. The former increases monotonically from ~ 10 K to ~ 85 K, while the latter of ~ 45 K does not change much resulting in a crossing of the two energy levels at x ≊ 0.6. The reported minimum in the superconducting transition temperature Tc at x ≊ 0.6 could be associated with the level crossing.

Zero field (ZF) and transverse field (TF) muon spin relaxation and rotation (μSR) study has been carried out in filled-skutterudite SmOs4Sb12 in order to investigate the magnetically robust heavy-fermion (HF) state and the weak ferromagnetic anomaly appearing below ∼2.5K. A large-amplitude oscillating signal appears in the ZF-μSR spectra at low temperatures, confirming that the weak ferromagnetic anomaly is an intrinsic bulk property. Two components with the fraction ratio of ∼2:1 exist both in the ZF-μSR spectra of the ferromagnetically ordered state and the TF-μSR FFT spectra in applied fields along the 〈001〉 direction. This observation can be explained consistently based on the most probable muon stopping site indicated from the value of the static nuclear dipolar width in Kubo–Toyabe function in the high-temperature ZF-μSR spectra. Analysis reveals that the spontaneous magnetic moment Ms lies along the 〈001〉 direction and the size of Ms is largely suppressed, indicating that the weak ferromagnetic moment is carried by itinerant heavy quasiparticles.

We have investigated the Fermi-surface (FS) properties in the Pr-based filled skutterudite PrOs4P12 and its reference compound LaOs4P12 by means of de Haas-van Alphen experiments and the band-structure calculations. The topology of FS in PrOs4P12 is close to that in the reference compound LaOs4P12, indicating a localized nature of 4f electrons in PrOs4P12. Whereas the localized nature of 4f electrons, we have confirmed a highly enhanced cyclotron effective mass of up to 18m(0) in PrOs4P12, which is enhanced about 3.8 times compared to that in LaOs4P12. No nesting property with q=(1,0,0) in the FS of PrOs4P12 has been confirmed in contrast to good nesting properties in PrFe4P12 and PrRu4P12 which exhibit unusual ordered states at low temperatures. A role of both the 4f electron's contributions and the FS nesting property for unusual phase transitions are discussed.

Measurements of the susceptibility and magnetization of an unconventional superconductor PrOs4Sb12 have been performed in order to study the vortex dynamics. This type of superconductor contains multi-component order parameter. Our results sheds light on the interplay between superconductivity and nuclear magnetism of Pr. These measurements have been performed down to a sub mK. We have not found out any indication of the nuclear ordering. We have observed two small decrease of susceptibility around 560mK, 300mK and a large dia-magnetization at Tc. The magnetization hysteresis loop is measured at cycling fields of ±700Oe. Avalanche-like anomalies appear around zero field below 150mK. These avalanches become frequent as decreasing temperature. Based on the property of domain wall in time-reversal symmetry(TRS) breaking superconductors, possible origins of these avalanches are discussed.

We have carried out the synchrotron powder diffraction and x-ray absorption experiments of a valence-fluctuated heavy fermion compound SmOs4Sb12. The size of the Sb cage which includes a Sm atom shows significant temperature dependence. This correlates with the temperature dependence of the Sm valence. However, the cage size shrinks with decrease of temperature although the averaged ionic radius becomes large. This anomalous temperature dependence suggests the correlation between the cage size and the hybridization of the 4f electron with the conduction electrons in SmOs4Sb12.

The lattice specific heat C-lat of La-based filled skutterudites LaT4X12 (T = Fe, Ru and Os; X = P, As, and Sb) has been systematically studied, and both the Debye temperature Theta(D) and the Einstein temperature Theta(E) of LaT4X12 were carefully estimated. We confirmed that a correlation exists between Theta(D) and the reciprocal of the square root of average atomic mass for LaT4P12, LaT4As12, and LaT4Sb12. The Theta(D) of filled skutterudites was found to depend mainly on the nature of the species X forming the cage. The temperature dependence of C-lat/T-3 for LaT4X12 exhibited a large broad maximum at low temperatures (10 - 30 K), which suggests a nearly dispersionless low-energy optical mode characterized by Einstein specific heat. Since no such broad maximum exists for the unfilled skutterudite RhP3, the low-energy optical modes are associated with vibration involving La ions in the X-12 cage (the so-called "guest ion modes"). The BE of filled skutterudites was found to roughly correspond to the energy of low-energy guest ion optical modes. Furthermore, a good correlation was shown to exist between Theta(E) and r(R-X) - r(R3+), where r(R-X) is the R-X distance and r(R3+) is the effective ionic radius of R3+. As r(R-X) - r(R3+) increased, Theta(E) was found to decrease.

The human body literally glimmers. The intensity of the light emitted by the body is 1000 times lower than the sensitivity of our naked eyes. Ultraweak photon emission is known as the energy released as light through the changes in energy metabolism. We successfully imaged the diurnal change of this ultraweak photon emission with an improved highly sensitive imaging system using cryogenic charge-coupled device (CCD) camera. We found that the human body directly and rhythmically emits light. The diurnal changes in photon emission might be linked to changes in energy metabolism.