Thermal conductivity of Relation between and δ

The effect of oxygen stoichiometry content δ and zinc doping (Formula presented) on the thermal conductivity κ of (Formula presented) compounds is investigated. Various experimental results for (Formula presented) and 0⩽δ⩽0.5 are analyzed by using a theoretical model for the electronic contribution to the thermal conductivity in the case of a two-dimensional (Formula presented)-wave superconductor with Van Hove singularities (VHS) in the density of states. It is shown that the data can be quite well reproduced by considering the effect of the position of these VHS from the Fermi level on the thermal conductivity peak observed below (Formula presented) From this analysis, a simple relation between (Formula presented) and δ can be extracted. We argue that this relation is correlated to the variation of the Cu(2) valence with oxygen content and Zn concentration, and that the Cu(2) valence controls the critical temperature of such cuprates, further strengthening the Van Hove scenario of high-(Formula presented) superconductivity. © 1997 The American Physical Society.