Cu-NMR study has been performed on the disordered spin-gap system Tl1−xKxCuCl3 In the high-field H > HC=∆/µB, where ∆ is the spin-gap, the hyperfine field becomes extremely inhomogeneous at low temperatures due to the field-induced magnetic order, indicating that the ordered spin state must be different from the pure TlCuCl3. In the low field H < HC, a saturating behavior in the longitudinal nuclear spin relaxation rate T −1 1 was observed at low temperatures, indicating existence of the magnetic ground state proposed to be Bose-glass phase by Fisher.

A diffraction experiment using a high energy x-ray was carried out on YbInCu4. Below the Yb valence transition temperature, the splitting of Bragg peaks was detected in higher-order reflections. No superlattice reflections accompanying the valence ordering were found below the transition temperature. These experimental findings indicate that a structural change from a cubic structure to a tetragonal structure without valence ordering occurs at the transition temperature. Such a structural change free from any valence ordering is difficult to understand only in terms of Yb valence degrees of freedom. This means that the structural change may be related to electronic symmetries such as quadrupolar degrees of freedom as well as the change in Yb valence.Valence degrees of freedom are always coupled with structural degrees of freedom because the ionic radius is changed by a change in the valence state. When valence ordering occurs in materials, the space group of their crystal structure can change because of the alignment of the ions with valence states. Meanwhile, when a valence change occurs without valence ordering, the unit cell volume is expected to change owing to the change in the ionic radius but the symmetry of the crystal structure is not expected to be changed by a valence transition. If a valence transition with a symmetric change but no valence ordering occurs, the discovery of such a valence transition would shed new light on the valence transition compounds.

We measured the electrical resistivity ρ of CeIr(In1-xCdx)5 under pressure for x = 0.05 and 0.10, which show the onset of superconductivity (SC) at Tsc onset ~ 0.9 K and antiferromagnetic transition at TN ~ 3.4 K. For x = 0.05, Tsc onset increases by applying pressure up to 2.8 GPa and zero resistivity is observed at Tsc ρ=0 above 2.4 GPa. For x = 0.10, the pressure dependence of TN shows peak at around 2 GPa and TN seems to be 0 K toward 3 GPa, where SC phase appears. The maximum value of Tsc ρ=0 is independent on amount of doped Cd, showing 1.35 K. We analyzed the temperature dependence of the electrical resistivity ρ for x = 0.05 and 0.10 under pressure using the following equation, ρ = ρ0 + AT n . This analysis revealed that ρ shows the sublinear temperature dependence (n < 1) in the wide temperature region above Tsc ρ=0 , and ρ0 decreases abruptly in the pressure region where Tsc ρ=0 indicates a maximum.

High-magnetic-field X-ray absorption spectroscopy of the heavy-fermion compound CeIrIn 5 has been conducted to clarify the valence state of Ce at the metamagnetic transition. The field-induced change in the X-ray absorption spectrum near the Ce-L 3 edge is found to be smaller than the resolution limit of the measurement, suggesting that no field-induced valence change larger than 0.005 takes place at 2 K up to 42 T.

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