Negative charge carriers in the 90 K plateau of REBa 2Cu 3O 7−δ

Abstract

Specific heat, thermopower and electrical resistivity in magnetic field were measured in the series of polycrystalline REBa 2Cu 3O 7−δ samples from the so-called 90 K plateau of T c versus δ dependence. Clear correlations between such electronic quantities as specific heat jump, Δ C p , thermopower at 300 K, S 300, and slope of the upper critical field, d H c2/d T, were observed for all the investigated samples. We proposed some possible explanation of the observed effects in terms of the simple theory of metals and Ginzburg-Landau-Abrikosov-Gorkov theory of type-II superconductors. This analysis suggests that in the REBa 2Cu 3O 7−δ superconductors with T c from the region of the 90 K plateau there exist charge carriers of negative sign, in addition to holes dominating the Hall effect. The electronic density of states of the negative charge carriers is the highest for δ ≈ 0 and substantially lower near the edge of the plateau. Its value is responsible for the changes of Δ C p , d H c2/d T and the negative component of S 300 in the region of the 90 K plateau.