Fumitaka Arai

Optical Study on Electronic Structure of Rare-Earth Sesquioxides.

Reflectivity spectra of nine rare-earth sesquioxide ( R 2 O 3 ; R = La, Pr, Nd, Sm, Eu, Er, Tm, Yb and Lu) single crystals have been measured in the photon energy range from 0.5 to 50 eV at 300 K. The fundamental optical absorption has been clarified in connection with the electronic structure of R 2 O 3 . The absorption due to an intra-atomic optical transition of R 4 f → R 5 d 6 s was observed in the same energy region as the charge transfer excitation of O 2 p → R 5 d 6 s in the energy range of 6–15 eV. The absorption structure of the R 4 f → R 5 d 6 s transition and the R 5 p → R 5 d 6 s transition are explained by using the crystal field splitting of the 5 d band and the multiplet structure of the 4 f n -1 final state in photoemission process. Fine structures due to the absorption of the R 4 f → O 3 s transition in the energy region of the O 2 p → O 3 s absorption were observed and also can be explained by the 4 f n -1 final state.

Mixed valence of praseodymium oxides

Abstract Reflectivity and resonant photoemission spectra of three kinds of Pr-oxide single crystals were measured to investigate the valence of the Pr-ion in Pr-oxides. The coexistence of the valence states of Pr 3+ and Pr 4+ in PrO 2 −δ was observed.

Resonant photoemission study of electronic structure of rare-earth sesquioxides

Electronic structures of ten kinds of rare-earth sesquioxide single crystals ( R 2 O 3 ; R =La, Pr, Nd, Sm, Eu, Gd, Er, Tm, Yb and Lu) were investigated by 4 d -4 f resonant photoemission measurement. The information of the electronic structure, especially the relative binding energy of 4 f state and O 2 p valence band, was obtained. The 4 d -4 f resonant photoemission spectra of valence band can be explained by multiplet structure of 4 f n -1 final state and the mixing between 4 f and O 2 p . The O 2 p valence band has 4 d -4 f resonance in La 2 O 3 that is in a typical 4 f 0 case. La 5 d character is considered to mix to the O 2 p valence band.

Optical and Photoelectrical Studies of Electronic Structure of R3Au3Sb4 (R=La, Ce and Pr)

The electronic structures of a magnetic semiconductor Ce 3 Au 3 Sb 4 and the related materials, La 3 Au 3 Sb 4 and Pr 3 Au 3 Sb 4 , have been investigated by reflectivity and resonant photoemission spectra. From the resonant photoemission spectra of Ce 3 Au 3 Sb 4 , the hybridization between the Ce4 f state and the Sb5 p valence band was found to be weak. This result is consistent with the electronic structure which is derived from the analysis of the optical data about the energy gap. The experimentally determined electronic structure is compared with a band calculation of La 3 Au 3 Sb 4 . The unoccupied 4 f state is concluded to be about 3 eV above the Fermi level, which is higher by 2 eV than the result of the band calculation. The exciton like absorption due to the transition from 4 f to 5 d states was observed. The intra-atomic Coulomb interaction between 4 f and 5 d states is thought to play an important role.

Optical Study of Electronic Structure and Nonmetal-Metal Transition of Gd2S3

Reflectivity spectra of a magnetic semiconductor material Gd 2 S 3 (=Gd 3- x V x S 4 , where V denotes vacancy and x =1/3) have been measured in the energy range from 2 meV to 40 eV at 9, 20, 77 and 300 K. From the comparison between the optical conductivity and the photoelectron spectra, the energy position and the shape of the occupied and the unoccupied electronic states were obtained. Above 77 K, this material showed a metallic reflectivity spectrum, but an energy gap of about 7 meV opened on the Fermi level below 20 K. The origin of the nonmetal-metal transition was concluded to originate from the creation of a magnetic polaron state.

Optical observation of energy gap of R3Au3Sb4 (R=La, Ce)

Reflectivity spectra of R 3 Au 3 Sb 4 (R=La, Ce) polycrystals were measured in the photon energy range from 5 meV to 40 eV at 6, 78 and 297 K. A narrow energy gap was observed for both materials. In La 3 Au 3 Sb 4 , it was seen that the energy gap of about 150 meV is an indirect one. The absorption due to the direct and allowed transition was observed around 0.7 eV. These results are consistent with the calculated band structure. In Ce 3 Au 3 Sb 4 , it was seen that the energy gap of about 70 meV is a direct one. The gap is considered to consist of the occupied 4 f state and the unoccupied 5 d state.

Optical spectra of CeAs and LaAs

Abstract Reflectivity spectra of CeAs and LaAs have been measured in the photon energy range from 2 meV to 32 meV at 6, 78 and 300 K. In CeAs, the effective electron number is small at 6 K and the Drude tail has been observed which is thought to originate from the conduction of the heavy fermion at 6 K. The absorption structure from the mixing state between Ce-4f and As-4p was resolved above 1 eV. The states splits into two with the splitting energy of 1.8 eV.

Spectrum of coherent synchrotron radiation

A spectrum of coherent synchrotron radiation was measured at wavelengths of from 0.16 to 3.5 mm. The experiment was carried out using the Tohoku 300-MeV linac, whose accelerating frequency was 2856 MHz. A bunch shape was estimated by Fourier analysis for this spectrum. This result agrees with that of simulation for the bunching process in the injector of the accelerator. The interference effects between radiation emitted by the successive bunches were observed by an interferometer. It was shown that every radiation had the same phase when it was emitted by a bunch.<<ETX>>

Resonant photoelectron spectra of Gd compounds

Abstract 4f resonant photoelectron spectra of three kinds of Gd compounds, GdB6, GdB4 and Gd2S3, have been measured in the excitation photon energy from 32 to 154 eV. The line shapes of the 4f state of these materials are different from one another. The origin of the difference is discussed.