Modeling And Photoabsorption Study of YPd2-xRhxB2C Superconductors
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Modeling And Photoabsorption Study of YPd2-xRhxB2C Superconductors L.-S. Hsu1, Y. K. Wang2, G. Y. Guo2, 3, Y.-J. Huang4, and M.-D. Lan4 1 Department of Physics, National Chang-Hua University of Education, Chang-Hua 50058, Taiwan, ROC 2 Department of Physics, National Taiwan University, Taipei 106, Taiwan, ROC 3 Synchrotron Radiation Research Center, Hsinchu 300, Taiwan, ROC 4 Department of Physics, National Chung Hsing University, Taichung 402, Taiwan, ROC ABSTRACT The electronic structures of six polycrystalline borocarbide superconductors YPd5-xRhxB3C0.4 (x=0, 0.05, 0.1, 0.15, 0.2, and 0.25) were studied by photoemission and photoabsorption spectroscopies and theoretical calculations. The valence-band (VB) photoemission spectrum is compared with the theoretical total and partial density-of-states (DOS) curves. The Pd L3-edge x-ray absorption near edge spectra (XANES) are compared with the calculated XANES spectra for these intermetallic compounds. The decrease of the superconducting transition temperatures (Tc) with addition of Rh dopant in these compounds is due to a decrease of the total DOS at the Fermi level (EF). INTRODUCTION The discovery of superconductivity with Tc up to 23 K in the RM2B2C (R=rare earth; M=Ni, Pd) quaternary intermetallic compounds [1-3] stimulated a new interest in materials other than high-Tc oxides. The substitution of Ni by other transition metals Fe, Co, and Ru in YNi2B2C was studied both theoretically and experimentally [4-6]. The Pd-based borocarbides were less studied, and controversy still exists for tetragonal or face-centered cubic structure for the 1-2-2-1 metastable phase [3,7,8]. First principles self-consistent band-structure calculation [9] of YPd2B2C suggested that the superconductivity is related to the presence of a narrow peak in the DOS at EF, with mixed Y d and Pd d character. The purpose of this study is to use photoemission spectroscopy and XAS at the Pd L3 edge to study the electronic structures of six Rh-doped YPd5-xRhxB3C0.4 (x=0, 0.05, 0.1, 0.15, 0.2, and 0.25) borocarbide superconductors. Theoretical calculations were also performed to compare with the results obtained from experiments. EXPERIMENT AND THEORY Six polycrystalline samples of borocarbide superconductors were arc-melted under 1 atm Ar. The total sample weight losses were less than 2%. They were then characterized by W8.13.1 Downloaded from https://www.cambridge.org/core. Columbia University Libraries, on 21 Aug 2017 at 22:42:53, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-731-W8.13
powder x-ray diffraction (XRD), energy-dispersive x-ray spectroscopy (EDX), and magnetic measurement using superconducting quantum interference device (SQUID). The XRD and EDX measurements [10] confirm that the samples are single phase of body-centered tetragonal structure, and the correct Rh concentration for the bulk materials. The Tc values of these superconductors from SQUID measurement [10] are shown in figure 1. Photoemission and photo
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