On the specific features and transformation of the band structure of mercury-based HTSC compounds

Abstract

A systematic analysis of the temperature dependences of the thermopower S(T) for different phases of the HgBa2Can−1Cu n O2n+2+δ family (n=1, 2, 3) at different doping levels is performed in the framework of a narrow-band phenomenological model. Quantitative estimates of the main parameters of the band responsible for conduction in the normal phase of HgBa2Can−1Cu n O2n+2+δ are given for optimally doped samples. The character of the variation in these parameters with an increasing number n of the copper-oxygen layers is discussed. A trend toward broadening of the conduction band with increasing n is revealed, which can be due to the increase of the density-of-states (DOS) peak near the Fermi level with an increasing number of the CuO2 layers responsible for the formation of the conduction band. It is found that an increase in the number n leads to an increase in the fraction of localized carriers in the band owing to a more defective structure observed in the more complex phases of HgBa2Can−1Cu n O2n+2+δ. The variations in the band-structure parameters in going from under-to overdoped compositions in the HgBa2Can−1Cu n O2n+2+δ family are also discussed.