Metal - dielectric transition and temperature dependence of the pseudo-gap in YBa2Cu3O7-delta single crystals: effect of pressure and oxygen nonstoichiometry

The effect of high hydrostatic pressure on the electric resistance in the ab plane of the oxygen-deficient YBa2Cu3O7-delta single crystals has been investigated. It is shown that the pressure-induced redistribution of the labile oxygen results in an intensified phase layering accompanied by structural relaxation processes within the experimental sample volume. A significant displacement of the temperature ranges that correspond to metal-dielectric type transitions and the pseudo-gap realization regime. The description of the excess conductivity as Delta sigma similar to(1 - T/T*)exp(Delta*(ab)/T) can be interpreted in terms of mean field theory where T* is the mean-field temperature of the super-conducting transition and the temperature dependence of the pseudo-gap is well described in the framework of the BCS-BEC crossover theory. Increasing the applied pressure results in the narrowing of the temperature range where the PG regime is realized, thus extending the area of linear p(T) dependence in the ab plane.