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

摘要

We present the results on the normal-state (the resistivity, rho, 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 Y1-xCaxBa2Cu3Oy with different oxygen content, double-substituted Y1-xCaxBa1.5La0.5Cu3Oy and Y1-xCaxBa2Cu3-zCozOy (z = 0.25, 0.4), as well as co-doped Y1-xCaxBa2-xLaxCu3Oy and Y1-xCaxBa2Cu3-xCoxOy. 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 rho (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 the 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. [References: 14]