Browsing by Author "Nachimuthu, P"

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A comparison between the Fehrenbacher-Rice and the Liechtenstein-Mazin models
(2000-11-01)
Liu, SJ
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Lin, JY
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Chen, JM
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Nachimuthu, P
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Luo, CW
Unoccupied electronic states of Y1-xPrxCu3O7-y (x = 0 - 1) thin films have been investigated using high-resolution polarization-dependent O K-edge x-ray absorption spectroscopy (XANES). After determining the hole distribution among different oxygen sites of the Pr-doped thin films, we compare the experimental data with the Fehrenbacher and Rice (FR) model and the Liechtenstein and Mazin (LM) model, both of which are based on the hybridization of Pr 4f(z(x2-y2)) and O 2p(pi) orbitals in PrBa2Cu3O7-y. Our experimental results are more consistent with the FR model.
Origin of size effect on superconductivity in (R-0.8 Pr-0.2)Ba2Cu3O7 studied by soft X-ray absorption spectroscopy
(2001-03-30)
Chen, JM
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Nachimuthu, P
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Lin, JY
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Hong, IP
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Chang, CF
O K-edge X-ray absorption near-edge structure (XANES) spectroscopy of (R-0.8 Pr-0.2)Ba2Cu3O7 (R = Y, Tm, Dy, Gd, Eu and Sm) has been performed to investigate the dependence of hole distribution on ionic size of the R3+ ions. Near the O Is absorption edge, pre-peaks at similar to 527.8 and similar to 528.5 eV are assigned to transitions into O 2p hole states located in the CuO3 ribbons and CuO2 planes, respectively. As deduced from O K-edge X-ray absorption spectra, the hole concentrations in the CuO2 planes decrease monotonically with increasing ionic size of the rare-earth elements. The present XANES results clearly demonstrate that the suppression of superconductivity in (R1-x Pr-x)Ba2Cu3O7 With ionic radius of the R3+ ions results predominantly from the hole-depletion effect. (C) 2001 Elsevier Science B.V. All rights reserved.
X-ray absorption near-edge structure of Pr1-xBa2+xCu3O7
(2000-11-01)
Yang, HD
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Hong, IP
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Chatterjee, S
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Nachimuthu, P
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Chen, JM
PrBa2Cu3O7 (Pr123) has attracted much attention due to its non-superconductivity and other anomalies. The very recent reports on superconducting Pr123, instead of putting an end on this issue, virtually stimulate more controversies. One of the proposed explanations for the recently observed superconductivity in Pr123 is that the samples could be Ba-rich Pr123. To investigate this possibility, we have prepared Pr1-xBa2+xCu3O7 With x=0 to 0.3. It is found that resistivity of the samples becomes smaller with increasing x, together with elongation of the c-axis. O K-edge x-ray absorption structure indicates an increase in the carrier concentration with Ba doping. However, carriers are introduced in a peculiar way rather than simply added into CuO2 planes.