Showing papers by "Shik Shin published in 1999"

Crystal-field splitting and the on-site Coulomb energy of La x Sr 1 − x TiO 3 from resonant soft-x-ray emission spectroscopy

Abstract: Resonant soft-x-ray emission spectroscopy was measured on ${\mathrm{La}}_{x}{\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{TiO}}_{3}$ $(x=0,0.05,0.10)$ in the $\mathrm{Ti}2p$ energy region. At the Raman scattering of the ${e}_{g}$ resonance, the $d\ensuremath{-}d$ transition whose Raman shift has an energy value of about 2.3 eV corresponds to the crystal-field splitting. On the other hand, at the ${t}_{2g}$ resonance, the $d\ensuremath{-}d$ transition whose Raman shift is about 2.2 eV is thought to be the transition reflecting half intra-atomic Coulomb energy.

Resonance effect on inverse-photoemission spectroscopy of CeRh 3 , CePd 3 , and CeSn 3

Abstract: The resonant inverse photoemission study (RIPES) at the Ce $4\stackrel{\ensuremath{\rightarrow}}{d}4f$ absorption edge of ${\mathrm{CeRh}}_{3},$ ${\mathrm{CePd}}_{3},$ and ${\mathrm{CeSn}}_{3}$ has been carried out. The RIPES spectra show the wide variety of the $4f$ electron character in these compounds, indicating the characteristic Kondo temperature and $4f$ electron number. The excitation energy dependence of $4f$-spectral resonance, especially in ${4f}^{2}$ final-state structure, indicates a large $4d\ensuremath{-}4f$ multiplet splitting and strict selection rule in the final state of the RIPES process. Constant final-state spectra of the ${f}^{1}$ final state show the $4f$ spin-orbit splitting components. A calculation is carried out by the impurity Anderson model with full multiplet effects and explains well the excitation energy dependence of the RIPES spectra.

Electron Energy-Loss Spectroscopy Study of the Metal-Insulator Transition in (V1-xCrx)2O3 (x=0.012)

Abstract: Electron energy-loss spectra of (V1-xCrx)2O3 (x=0.012) at the antiferromagnetic insulating (AFI), paramagnetic metallic (PM) and paramagnetic insulating (PI) phases have been measured using a high-resolution transmission electron energy-loss spectroscopy (EELS) microscope. The changes in the EELS spectra at the transition from the PM phase to the AFI phase are interpreted in a similar manner to the case of V2O3 [Jpn. J. Appl. Phys. 37 (1998) 584]. The change in the electronic structure at the transition from the PM phase to the PI phase (Mott transition) was revealed for the first time. A sharp peak observed at 1.0 eV in the PM phase did not appear in the PI phase. The t2g peak of the O 1s → V 3d(t2g) EELS spectra shows an energy increase of 0.5 eV at the transition from the PM phase to the PI phase. This increase is interpreted to occur by the splitting of the bonding egπ band, which is partially filled in the PM phase, into the fully occupied lower band and the unoccupied upper band, and by the lifting of the unoccupied band to an energy higher than the Fermi level in the PM phase. The t2g peak also shows a decrease in intensity but an increase in the full width at half-maximum (FWHM) at the transition. The decrease in intensity occurs due to the decrease of the hybridization of the V 3d with the O 2p orbitals resulting from an increase of the V–O distance. The increase in the FWHM results from the lifting of the a1g* band due to the decrease of the lattice constant cH and the splitting of the egπ and egπ* bands each into two bands due to electron correlation.

Electronic Structure of BP Studied by Resonant Soft X-ray Emission Spectroscopy

Abstract: The B1 s and P2 p soft x-ray emission of BP has been measured using monochromatic synchrotron radiation as an excitation source. The band-gap energy was estimated to be about 2.1 eV which is in good agreement with other experiments. The emission bands which reflect the partial density of states in the valence band showed resonant aspects. The spectral profile was interpreted by a momentum conservation approach.

Proton Diffusion in SrZr 0.95Y 0.05O 3 Observed by Quasielastic Neutron Scattering

Abstract: Proton diffusion was observed in Y-doped SrZrO 3 ceramics above 500°C by quasielastic neutron scattering. The line width of the quasielastic component varies with energy transfer Q and temperature. The temperature dependence is well elucidated by the thermal activation-type proton migration with activation energy of 0.2 eV. The observed hopping distance was 1.7 A, which is comparable to one of the distances between two proton sites.

Observation of the coherence transition into a collective dense Kondo state by resonant inverse photoemission spectroscopy

Abstract: By the resonant inverse photoemission spectroscopy (RIPES), we study the crossover from mixed-valent to heavy-fermion and Kondo regime in ${\mathrm{CeCoGe}}_{3\ensuremath{-}x}{\mathrm{Si}}_{x}$ $(0l~xl~3).$ We have measured the RIPE spectra as functions of composition and temperature. The strong composition dependence of $4f$ state (``${f}^{1}$ peak'') just above the Fermi level shows that the localized $4f$ electrons in the compound become itinerant due to the enhanced Kondo effect within the range $1.0l~xl~1.5.$ Temperature dependence of the ${f}^{1}$ peak indicates a transition from the paramagnetic state at room temperature to a coherent Fermi-liquid regime at low temperatures where the Kondo effect dominates. The most remarkable variation of the spectra has been observed above 200 K with increasing temperature in ${\mathrm{CeCoSi}}_{3}$ which has a very high Kondo temperature ${T}_{K}$ of about 900 K. This suggests that the change in the $4f$-electronic state of ${\mathrm{CeCoSi}}_{3}$ may be scaled by the coherence transition temperature rather than ${T}_{K}.$

Absence of U 5f band states in resonant photoemission spectra of UPd 2 Al 3

Abstract: The U 5f spectral weight of UxLa12xPd2Al3 (x50.1, 0.25, 0.6, and 1.0 ! is obtained by the resonant photoemission spectroscopy ~RPES!, and is compared with the results of the band-structure calculations. We have found that the spectrum of UPd 2Al3 (x51) could not be reproduced by the calculated U 5 f density of states in shape and position, even if the contribution from U 6 d states is considered. Moreover, the essential spectral shape did not change until x50.1, where most of the uranium atoms are substituted with lanthanum atoms. All these results indicate that the U 5 f band states are not observed in the RPES spectrum of UPd 2Al3, and the single site effects govern it. @S0163-1829 ~99!01215-1#

Contrasting Kondo behavior and resonant inverse photoemission spectra of CeTSi3 and CeTGe3 (T=Rh and Ir)

Abstract: CeTSi3 and CeTGe3 (T=Rh and Ir) were investigated by measuring the magnetic susceptibility, specific heat, electrical resistivity, the resonant inverse photoemission (RIPES) and MIV,V X-ray absorption spectra (XAS). The germanides showed a very weak Kondo effect, but the silicides exhibited a negatively large Weiss temperature (≈−130 K) and a ln T dependence of magnetic resistivity above 100 K, suggesting that they are Kondo-lattice compounds with a high Kondo temperature TK (≈100 K). The Curie–Weiss law suggests that Ce atoms in these compounds remain close to 3+ down to about 150 K in spite of their high TK. Both RIPES and MIV,V XAS support their apparently stable valency.

Symmetry analysis of the Fermi surface states of Sr2RuO4 by display-type photoelectron spectroscopy

Abstract: The Fermi surface of the noncuprate superconductor Sr 2 RuO 4 has been studied in detail by two-dimensional angle resolved photoelectron spectroscopy (2D-ARPES) using a display-type electron spectrometer and a linearly polarized synchrotron radiation. The existence of the large Fermi surfaces agrees with previous band calculations and conventional ARPES measurements. From the comparison of the observed photoelectron intensity distribution of the Fermi surface with that of the simulation for atomic orbitals, the symmetry of the atomic orbitals composing the Fermi surfaces is revealed to be the d e ; d x y , d y z , d z x -like in contrast to the d x 2 - y 2 -like orbital in the cuprate high- T c super conductor. The possibility of the existence of the extended van-Hove singularity just below the Fermi level, which was suggested by recent conventional ARPES measurements, is also discussed.

Resonant inverse photoemission study on cerh3 at ce 4d absorption edge

Abstract: The resonant inverse photoemission study (RIPES) of CeRh 3 has been carried out at Ce 4d→4f absorption edge. The 4f cross section increases drastically when the excitation energy is tuned to absorption edge. The line shape of 4f 2 state changes by the resonance effect because of its multiplet structure. The RIPES of CeRh 3 which is in the valence fluctuation (VF) region shows the strong f 1 intensity. The energy position of f 1 peak of CeRd 3 is about 1 eV, which reflects the extremely high Kondo temperature of CeRh 3 .