Browsing by Author "Lin, J.-Y."

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Dichotomy of photoinduced quasiparticle on CuO2 planes of YBa2Cu3O7 directly revealed by femtosecond polarization spectroscopy
(2007-08-01)
Luo, C. W.
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Chen, L. Y.
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Lee, Y. H.
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Wu, K. H.
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Juang, J. Y.
The dichotomy of photoinduced quasiparticle dynamics in the anisotropic high T, superconductors (YBa2CU3O7) is revealed by using the orientation-resolved ferntosecond reflection spectroscopy in the specially designed thin films. The transient reflectivity Delta R/R along the ab diagonal and b axis are totally different in the slow relaxation process which relates to the opening of the superconducting gap. In addition, the distribution of the temperature evolution of Delta R/R on the CuO2 planes of YBa2Cu3O7 may indicate the d-wave symmetry of the superconducting gap in high T, superconductors. (c) 2007 American Institute of Physics.
Effect of Mn impurities on the superconductivity in NaxCoO2 center dot yH(2)O
(2007-09-01)
Chen, Y.-J.
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Liu, C.-J.
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Wang, J.-S.
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Lin, J.-Y.
;
Sun, C. P.
To shed light on the symmetry of the superconducting order parameter in NaxCoO2 center dot yH(2)O, the Mn doping effects are studied. X-ray absorption spectroscopy verifies that the doped Mn impurities occupy the Co sites and are with a valance close to +4. Impurity scattering by Mn is in the unitary limit that, however, does not lead to strong T-c suppression. This absence of the strong impurity effects on T-c is inconsistent with the simple picture of a sign-changing order parameter. Coexistence of the s-wave superconducting order parameter and the nodal one is proposed to reconcile all the existing experiments and has been implied by the specific heat experiments.
Fabrication and X-ray absorption NaxCoO2 spectroscopy in layered cobaltate thin films
(2007-03-01)
Chang, W. J.
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Lin, J.-Y.
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Chung, T. Y.
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Chen, J. M.
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Hsu, C.-H.
NaxCoO2 (x similar to 0.68) thin films were fabricated on sapphire (0 0 0 1) substrates via the lateral diffusion of sodium into Co3O4 (1 1 1) films, which were grown by pulsed-laser deposition. From the results of X-ray diffraction and in-plane resistivity rho(ab), the single phase and the metallic behaviors of these NaxCoO2 films can be identified. For the same sodium content x, rho(ab) is consistent with that of single crystals. In addition, the O 1s X-ray absorption near edge spectra of thin films are measured and compared with those of single crystals. (c) 2006 Elsevier B.V. All rights reserved.
Induced magnetic moment by Mn doping in NaxCo1-zMnzO2 center dot yH(2)O
(2007-03-01)
Lin, J.-Y.
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Chen, Y.-J.
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Liu, C.-J.
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Wang, J.-S.
;
Sun, C. P.
Impurity effects on NaxCoO2 (.) yH(2)O are studied by Mn doping. Spectroscopic evidence reveals that the doped Mn ions occupy the Co sites and the valence is +4. The magnetic local moment induced by Mn doping was observed and mu(eff) 3: 20 mB. The induced local moment could lead to magnetic pair-breaking and is likely to be responsible for the Tc suppression by Mn impurities in Na(x)Co(1-z)MnzO(2) (.) yH(2)O. (c) 2006 Elsevier B. V. All rights reserved.
Specific heat of Mn-doped NaxCoO2 center dot yH(2)O
(2007-09-01)
Lin, J.-Y.
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Chen, Y.-J.
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Liu, C.-J.
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Wang, J.-S.
;
Sun, C. P.
C(T) of NaxCo0.99Mn0.01O2 center dot yH(2)O is studied to reveal more details on the nature of the doped Mn ions and the T-c suppression. The extra specific heat contribution in NaxCo0.99Mn0.01O2 center dot yH(2)O manifests the induced local magnetic moment due to Mn doping. The absence of the superconducting transition peak in C(T) of NaxCo0.99Mn0.01O2 center dot yH(2)O suggests a reduced superconducting volume fraction. (C) 2007 Elsevier B.V. All rights reserved.