On the transformation of the normal-state band spectrum of Tl-based HTSC’s with increasing number of CuO2 layers and doping level

In this paper we present the results of complex quantitative analysis of thermopower data for Tl-based high-temperature superconductors in the framework of a phenomenological narrow-band model. On the basis of this model we have determined the parameters characterizing the band structure and properties of the charge-carrier system in the normal-state for samples of different phases and with different substitutions. The common tendencies in variations of these parameters with changing sample composition were revealed. We have analyzed the band spectrum transformation with increasing number of CuO2 layers for n = 1–4 Tl-based HTSC’s with the optimally-doped compositions as well as in the underdoped and slightly overdoped regimes. Possible mechanisms of modification of the band responsible for the conduction process were proposed and their relative role in different cases was discussed in a comparison with the variations of the superconducting properties.