In situ temperature-dependent x-ray-absorption spectroscopic studies for the mercury-based superconductors

In situ temperature-dependent x-ray-absorption spectroscopic studies have been carried out for the mercury-based cuprate superconductor Hg0.5Tl0.5Ba2(Ca0.86Sr0.14)(2)Cu3O8+delta, in order to examine the evolution of elec tronic and geometric structures below and above the superconducting transition temperature (T-c=128 K). According to the in situ Cu K-edge x-ray-absorption neat-edge structure (XANES) analyses, it is found that the copper valence is remarkably enhanced with a partial formation of Cu(III) ions in the superconducting state, reflecting a lattice instability around copper upon the superconducting transition, which is also confirmed by the in situ Hg L-III- and Tl L-III-edge XANES analyses. Such a finding underlines that the phonon-mediated pairing mechanism makes a significant contribution to the superconductivity of the Hg-based cuprates. On the other hand, the systematic Cu K-edge XANES spectroscopic studies for a series of Hg1-xTlxBa2(Ca0.86Sr0.14)(n-1)CunO2n+2+delta (x=0 and 0.5; n=1, 2, and 3) superconductors have also been performed, which allows us to determine the effects of the Tl substitution and the number of (Cu-O) sheet per formula unit (n) on the hole concentration df the copper-oxygen layer.