Determination of the parameters of the normal state in doped yttrium high-temperature superconductors from thermopower coefficients in terms of different models of electron transport

The temperature dependences of the thermopower coefficient for two systems of doped yttrium high-temperature superconductors Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_y$ ($x$ = 0.1–0.6) and Y$_{1-x}$Ca$_x$Ba$_{1.5}$La$_{0.5}$Cu$_3$O$_y$ ($x$ = 0.05–0.3) have been analyzed using three models of electron transport, i.e., the Xin two-band model, the two-band model with an additional term linear in temperature, and the narrow-band model. For parameters of different models with a similar physical meaning, identical tendencies have been revealed in their variation with an increase in the dopant content. The mechanisms of influence of the dopants under investigation on the parameters of the band spectrum and the systems of charge carriers have been examined. It has been demonstrated that the revealed features of the dynamics of the Fermi level in the Y$_{1-x}$Ca$_x$Ba$_{1.5}$La$_{0.5}$Cu$_3$O$_y$ system are explained by the formation of an additional peak in the density of states upon doping with calcium, and the energy position of this peak is estimated.