Influence of pressure on the critical temperature and resistivity of Y0.77Pr0.23Ba2Cu3O7-δ single crystals

In the present work, we investigated the influence of high hydrostatic pressure up to 11 kbar on the conductivity in the basal ab-plane of Y1-xPrxBa2CU3O7-delta single-crystalline samples medium-doped with praseodymium (x approximate to 0.23). It was found that, in contrast to the pure YBa2Cu3O7-delta with the optimal oxygen content, the application of high pressure leads to phase separation in the basal plane of Y0.77Pr0.23Ba2Cu3O7-delta single crystals. Possible mechanisms of the effect of praseodymium doping and high pressure on the two-step transition to the superconducting state are discussed. It was established that in the normal state, there is a conductivity of the metallic type, limited by the scattering of phonons (Bloch-Gruneisen regime) and defects. The fluctuation conductivity is considered within the Lorentz-Doniach model. Hydrostatic pressure, accompanied by a decrease in anisotropy, leads to a decrease in the residual and phonon resistances. The Debye temperature and coherence length are independent of pressure. The applicability of the McMillan formula in the presence of significant anisotropy is discussed. The excess conductivity Delta sigma(T) obeys an exponential temperature dependence in the broad temperature range T-f < T < T*. The dependence Delta sigma(T) similar to (1- T/T*)exp(Delta*(ab)/T) is interpreted in terms of the mean-field theory, where T* is the mean-field temperature of transition to the pseudogap state; and the temperature dependence of the pseudogap is satisfactory described within the BCS-BEC crossover theory.