Ca effect on the normal-state and superconducting properties of Y-based HTS

TLDR: In this paper, the results on the normal state (the resistivity, ϱ, thermopower, S, and Hall coefficient, R ) and superconducting properties of high T c compounds of the Y-123 family doped by calcium were presented.

Abstract: We present the results on the normal-state (the resistivity, ϱ, thermopower, S , and Hall coefficient, R ) and superconducting properties of high- T c compounds of the Y-123 family doped by calcium. We have studied single-doped Y 1− x Ca x Ba 2 Cu 3 O y with different oxygen content, double-substituted Y 1− x Ca x Ba 2− x La x Cu 3 O y and Y 1− x Ca x Ba 2 Cu 3− z Co y O y . ( z =0.25, 0.4), as well as co-doped Y 1− x Ca x Ba 2− x La x Cu 3 O y and Y 1− x Ca x Ba 2 Cu 3− x O y . Such a complex study allowed us to reveal the general features of the Ca effect in Y-123. The results on the normal-state transport properties have been analyzed in the framework of a narrow-band model assuming the existence of a sharp peak of the density-of-states near the Fermi level. Within this model we were able to describe all the ϱ ( T ), S ( T ), and R ( T ) dependences, and to determine the parameters characterizing the charge-carrier system in the normal state. Analyzing the doping influence on the T c value, transport coefficients' behavior, and the band structure parameters we have shown that all specific features of the Ca effect can be explained within an assumption on the introducing of additional Ca-induced states into the band responsible for the normal-state and superconducting properties of Y-123.