[en] Very high resolution and bright soft X-ray light is supplied with high stability and enough photon flux by the twin-helical undulator beam line BL25SU of SPring-8. Either helicity light with very high circular polarization is emitted on the same optical axis. The fundamental radiation can cover the hν region from 0.22 to 3 keV, among which the hν region below 2 keV is covered by a constant deviation angle monochromator with varied line spacing plane gratings (VLSPGM). The content of the higher order light is less than 1%. Accurate evaluation of the energy resolution of the VLSPGM is done by photoemission of the Fermi edge of Au. By using a grating with a central groove density of 600/mm, a resolution of better than 15,000 is realized at 870 eV, whereas a resolution of better than 20,000 is realized by using a grating with 1000/mm central groove density. Three experimental stations for solid state spectroscopy are permanently set up in tandem on BL25SU: (1) high resolution photoemission (2) magnetic circular dichroism of core absorption (3) two dimensional photoelectron diffraction. Behind (3) can be installed another instrument such as a spin polarized photoemission or a photoelectron emission microscope. High resolution bulk sensitive photoemission has become a reality above several hundred eV. The photoemission resolution near 1 keV is better than 100 meV. The status of the beam line and typical research activities are reported

[en] The bulk sensitivity of the high energy photoelectron spectroscopy (PES) in the soft and hard X-ray regions is gradually recognized to be essential for studying the electronic structures of strongly correlated electron systems with different surface and bulk electronic structures. With increasing hν, the kinetic energy (E_K) of photoelectrons is increased with realizing longer inelastic mean free path. Studies of three-dimensional genuine bulk band dispersions and bulk Fermiology are only possible by the soft X-ray angle resolved PES (ARPES). Examples are given for Nd_2-xCe_xCuO₄ and CeRu₂X₂(X: Si, Ge). The temperature dependence of the Yb 4f spectra provides useful information on valence fluctuation and Kondo resonance. The applicability of the single impurity Anderson model (SIAM) and its limit is discussed in the examples of Yb_1-xLu_xAl₃ and YbAl₃. The importance of the bulk sensitivity is also demonstrated by the soft and hard X-ray PES for SmOs₄Sb₁₂. When E_K becomes very large, the nucleus (ion) recoil effects become observable on the core photoelectron emission from light elements. The example is shown for Yb_7/8Lu_1/8B₁₂ and the influence of the recoil effects for the future high energy ARPES is briefly discussed. (authors)

[en] We investigate dynamical properties of the half-magnetization plateau in S = 1 bond-alternating spin chains. Dynamical structure factors calculated by the exact diagonalization method are compared with the dispersion curves of low-lying excitations obtained by a cluster expansion technique. We find that in the half-magnetization plateau the quintet excitation forms the lowest-lying excitation. The field dependence of the critical exponents of the spin correlation functions are further investigated. On the basis of the results, characteristics of the half-magnetization plateau are discussed

[en] Absorption spectra of solid H₂ and D₂ are measured in the range 10-40 eV at 2K for the first time, using synchrotron radiation. The spectra can be divided into two components; exciton and interband transitions. The exciton absorption consists of bands corresponding to molecular transitions, and vibrational structures are observed in the first exciton band of solid H₂. (author)

[en] Electronic and magnetic states of CeCo_5-xB_x are studied element-specifically by means of high-resolution bulk-sensitive resonant photoemission spectroscopy (RPES) and soft X-ray absorption magnetic circular dichroism (MCD). Judging from MCD of the ferromagnetic CeCo₅, the spins of Ce 4f and Co 3d electrons couple antiferromagnetically with each other. RPES spectra show that the Ce 4f states are itinerant and form strongly mixed bands with the Co 3d states

[en] We investigate the Kondo effect in disordered electron systems using a finite-temperature quantum Monte Carlo method. Depending on the position of a magnetic impurity, the local moment is screened or unscreened by the spin of the conduction electron. The results indicate that the Kondo temperature has a spatial distribution. We show that the distribution of the Kondo temperature becomes wide and the weight at T_K = 0 becomes large as randomness increases. When randomness increases, the average susceptibility exhibits a logarithmic divergence, indicating that the observable susceptibility shows a non-Fermi-liquid behaviour at low temperatures

[en] Anderson Hamiltonian parameters for mixed-valence YbAl₃ were determined from the magnetic susceptibility, photoelectron-spectroscopy, and bremsstrahlung-isochromat-spectroscopy data. The 4f/sup 13/→4f/sup 14/ electron affinity energy is ∼0.5 eV and the hybridization between Yb 4f and Al conduction electrons is ∼0.05 eV, both of which are larger than conventional estimates. This hybridization and the resulting Kondo resonance are considered to play important roles for the anomalous properties of valence-fluctuating Yb compounds, as in the case of Ce compounds

No abstract available

[en] The use of circularly polarized light in the soft X-ray region is very powerful for the study of magnetic properties of materials. In particular, the magnetic circular dichroism of core absorption spectra (X-MCD) with high resolution and high accuracy provides useful information on the spin and orbital contribution to the magnetic moment. Information on the band structures is also obtained. Typical X-MCD results are reported for Pd-Fe alloys, Co₂YSn(Y=Ti, Zr, Nb) Heusler alloys, Fe_xTiS₂ intercalated material as well as dilute magnetic semiconductor Ga_1-xMn_xAs

[en] Full text:The metal-insulator (MI) transition in quasi- one-dimensional compound V₆O₁₃ has been investigated by photoemission spectroscopy (PES) and optical study. The PES study was utilized synchrotron radiation (SR) at the beam line BL25SU in SPring-8. The optical study was performed by using a laboratory system and SR at BL7B in UVSOR. V₆O₁₃ has three different crystallographic sites for vanadium iron. The nominal valence numbers of vanadium are changed through the MI transition accompanied by a structural change at 150 K. Another phase transition, considered as an antiferromagnetic order, occurs at 55 K. In this study, a change of electronic band structure in the chain-direction is observed up to 2 eV in the PES spectra. The energy gap between E_F and the occupied state is estimated as ∼ 0.15 eV in the insulating state. The temperature change in optical conductivity also represents first-order MI transition behavior. The energy regions of spectral change through the MI transition are different between the b parallel and b perpendicular directions. The energy gap observed in optical conductivity is about 0.2 eV along the b axis where photoexcitation occurs from the occupied to unoccupied states