NEGATIVE CHARGE-CARRIERS IN THE 90-K PLATEAU OF REBA(2)CU(3)O(7-DELTA)

Specific heat, thermopower and electrical resistivity in magnetic field were measured in the series of polycrystalline REBa(2)Cu(3)O(7-delta) a samples from the so-called 90 K plateau of T-c versus delta dependence. Clear correlations between such electronic quantities as specific heat jump, Delta C-p, thermopower at 300 K, S-300, and slope of the upper critical field, dH(c2)/dT, 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(2)Cu(3)O7-delta 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 delta approximate to 0 and substantially lower near the edge of the plateau. Its value is responsible for the changes of Delta C-p, dH(c2)/dT and the negative component of S-300 in the region of the 90 K plateau.