STRUCTURE AND SUPERCONDUCTING PROPERTIES OF Y1-XPRXBA2CU3OX

Two mechanisms, magnetic pair breaking and localization of charge carr iers, are generally used in the attempt to explain the suppression of superconductivity in Y1-xPrxBa2Cu3Ox. The application of both is unsat isfactory, and this makes the absence of superconductivity in PrBa2Cu3 Ox one of the most long-standing problems of HTSCs. We give a new insi ght into this problem by considering principally a new mechanism of su ppression based on the Pr-O resonance. This resonance can be described as the oscillation of the O ion in the CuO2 plane near its equilibriu m position, and this oscillation arises when the distance between O an d Pr becomes close to the critical one (2.38 Angstrom) for the realiza tion of the vibronic state. The vibronic state unites the electronic a nd nuclear modes into a motion with a broad spectrum. In the vibronic state, the 4f configuration of Pr ceases to be isolated, and its magne tic moment spreads on the whole Pr-O complex. Analysis of structural d ata obtained by neutron diffraction and x-ray absorption fine structur e measurements shows that, during oxygen oscillation, Pr resonates bet ween the states of different valence with a period of less than 10(-13 ) s. Because this is less than the lifetime of a Cooper pair, the comp etition between the magnetism of the vibronic state and superconductiv ity makes the creation of a Cooper pair energetically unfavourable.