X-ray photoemission studies of Zn doped Cu 1− xTl xBa 2Ca 2Cu 3− yZn yO 10− δ ( y = 0, 2.65) superconductors

Abstract

The X-ray photoemission (XPS) measurements of Cu 1− x Tl x Ba 2Ca 2Cu 3− y Zn y O 10− δ ( y = 0, 2.65) superconductors have been performed and compared. These studies revealed that the charge state of thallium in the Cu 0.5Tl 0.5Ba 2O 4− δ charge reservoir layer in Zn doped samples is Tl 1+, while it is a mix of Tl 1+ and Tl 2+ in Zn free samples. The binding energy of Ba atoms in the Zn doped samples is shifted to higher energy, which when considered along with the presence of Tl 1+ suggested that it more efficiently directed the carriers to ZnO 2 and CuO 2 planes. The evidence of improved inter-plane coupling witnessed in X-ray diffraction is also confirmed by XPS measurements of Ca atoms in the Zn doped samples. The shift of the valance band spectrum in these Zn doped samples to higher energies suggested that the electrons at the top edge of the valance band were tied to a higher binding energy (relative to samples without Zn doping), which most likely resulted in a much lower energy state of the system in the superconducting state. The stronger superconducting state arising out of these effects is witnessed in the form of increased T c( R = 0), J c and the extent of diamagnetism in the final compound.