Zinc Doping Effect on the Thermopower Behavior and the Modification of the Normal-State Energy Spectrum in the YBa2Cu3Oy System

In this paper, we have experimentally investigated the effect of zinc doping on the thermopower, S, behavior in the YBa
2
Cu
3
O
y
system. The character of the modification of the S(T) dependences under increasing zinc content was revealed and discussed in comparison with cases of other substitutions in this system. The experimental results were quantitatively analyzed on the basis of a narrow-band model that allowed us to determine the values of the main parameters of the energy spectrum and charge-carrier system in all the studied samples. It was observed that zinc doping strongly suppressing the superconducting properties of the YBa
2
Cu
3-x
Zn
x
O
y
system results simultaneously in a significant modification of the energy spectrum in the normal state inducing an appearance of the conduction band asymmetry. Possible mechanism of the observed energy spectrum transformation is discussed.