The study on the spin gap phenomenon in oxygen deficient YBa2Cu3O6+delta and Ca-doped Y1-xCaxBa2Cu3O6+delta superconductors

The understanding of the spin gap phenomenon in the normal state of the hig h temperature superconductors can provide the mechanism of the high tempera ture superconductivity. A specific function of thermal excitation for quasi particles was introduced based on the experimental relationship between res istivity and temperature. This specific function describes the deviation in resistivity from the T-linear relationship w.r.t. the normal state of the high temperature superconductors. With this function, the spin gap is natur ally introduced. Our experimental results indicate that the spin gap behavi or is closely related not only to the oxygen deficiency but also to the str uctural change in the a-b plane. Furthermore, we found that the crossover f rom anomalous metallic state to spin gap state takes place within a tempera ture range T-S < T < T*, which depends on the oxygen content and the Ca-dop ing level. Pressure effects on the spin gap phenomenon in bulk samples of o xygen-deficient YBa2Cu3O6+delta and Ca-doped Y1-xCaxBa2Cu3O6+delta were als o investigated. Under high hydrostatic pressure the spin gap behavior is al so severely influenced by the contraction of the a-b plane due to the press ure.