Photoemission Study of Rare-Earth Ditelluride Compounds (ReTe_2 : Re = La, Pr, Sm, and Gd)

We have investigated the electronic structure of LaFeAsO$_{1-x}$F$_{x}$ (x = 0; 0.1; 0.2) by angle-integrated photoemission spectroscopy and local density approximation (LDA) based band structure calculations. The valence band consists of a low energy peak at E = -0.25 eV and a broad structure around E = -5 eV in qualitative agreement with LDA. From the photon energy dependence of these peaks we conclude that the former derives almost exclusively from Fe 3d states. This const...

The strain effect from a substrate is an important experimental route to control electronic and magnetic properties in transition-metal oxide (TMO) thin films. Using hard x-ray photoemission spectroscopy, we investigate the strain dependence of the valence states in LaNiO$_{3}$ thin films, strongly correlated perovskite TMO, grown on four substrates: LaAlO$_{3}$, (LaAlO$_{3}$)$_{0.3}$(SrAl$_{0.5}$Ta$_{0.5}$O$_{3}$)$_{0.7}$, SrTiO$_{3}$, and DyScO$_{3}$. A Madelung potential a...

We report a photoemission and x-ray absorption study on Au1-xPtxTe2 (x = 0 and 0.35) triangular lattice in which superconductivity is induced by Pt substitution for Au. Au 4f and Te 3d core-level spectra of AuTe2 suggests a valence state of Au2+(Te2)2-, which is consistent with its distorted crystal structure with Te-Te dimers and compressed AuTe6 otahedra. On the other hand, valence-band photoemission spectra and pre-edge peaks of Te 3d absorption edge indicate that Au 5d ba...

We investigate the topological superconductor candidate UTe$_2$ using high-resolution valence-band resonant inelastic x-ray scattering at the U $M_{4,5}$-edges. We observe atomic-like low-energy excitations that support the correlated nature of this unconventional superconductor. These excitations originate from the U $5f^2$ configuration, which is unexpected since the short Te2-Te2 distances exclude Te2 being 2-. By utilizing the photoionization cross-section dependence of t...

We have investigated the electronic structure of electron-doped Sr$_{2-x}$La$_x$FeMoO$_6$ ($x$=0.0 and 0.2) by photoemission spectroscopy and band-structure calculations within the local-density approximation+$U$ (LDA+$U$) scheme. A characteristic double-peak feature near the Fermi level ($E_{\rm F}$) has been observed in the valence-band photoemission spectra of both $x$=0.0 and 0.2 samples. A photon-energy dependence of the spectra in the Mo 4$d$ Cooper minimum region com...

We have performed a systematic angle-resolved photoemission spectroscopy (ARPES) study of the high-Tc cuprates La2-xSrxCuO4, ranging from the underdoped insulator to the superconductor to the overdoped metal. We have revealed a systematic doping evolution of the band dispersions and (underlying) Fermi surfaces, pseudogap and quasi-particle features under the influence of strong electron-electron interaction and electron-phonon interaction. The unusual transport and thermodyna...

The electronic structure of double perovskite Pr2MnNiO6 is studied using core x-ray photoelectron spectroscopy and x-ray absorption spectroscopy. The 2p x-ray absorption spectra show that Mn and Ni are in 2+ and 4+ states respectively. Using charge transfer multiplet analysis of Ni and Mn 2p XPS spectra, we find charge transfer energies {\Delta} of 3.5 and 2.5 eV for Ni and Mn respectively. The ground state of Ni2+ and Mn4+ reveal a higher d electron count of 8.21 and 3.38 re...

The photo-induced band structure variation of a rare-earth-based semiconductor, samarium monosulfide (SmS), was investigated using high-harmonic-generation laser-based time-resolved photoelectron spectroscopy. A nonlinear photo-induced band shift of the Sm 4f multiplets was observed. The first one is a shift to the high-binding-energy side due to a large surface photovoltage (SPV) effect of approximately 93 meV, comparable to the size of the bulk band gap, with a much longer ...

Resonant valence-band X-ray photoelectron spectra (ResPES) excited near 2p$_{3/2}$ core level energies, 2p X-ray photoelectron spectra (XPS) and L$_{3,2}$ X-ray absorption spectra (XAS) of Ti and Mn in single crystal of 1T-Mn$_2$TiSe$_2$ were studied for the first time. The ionic-covalent character of bonds formed by Mn atoms with the neighboring Se atoms in the octahedral coordination is established. From the XPS and XAS measurements compared with results of atomic multiplet...

Hard x-ray photoemission and optical spectroscopies have been performed on YbS and Yb metal to determine the precise $f$-electron occupation. A comparison of the photoemission spectra with the energy loss functions in bulk and surface, obtained from optical reflectivity, enables us to distinguish between the energy loss satellite of Yb$^{2+}$ peak and Yb$^{3+}$ multiplet. The results clearly indicate a purely divalent Yb state except for the surface of YbS. We demonstrate tha...