Strong Localization Effect of Oxygen Deficiency on Carriers in T1 Based Superconductors

Investigation on the effect of Fe-doped T1-1223 superconductors has been carried out by the simultaneous measurements of the spectra of positron annihilation lifetime and Doppler broadening of position annihilation,together with the measurement of Hall coefficient. The results of samples with different doping level show that the occupation of Fe atoms on Cu sites results in a linear decrement of superconducting transition temperature. The electron concentration in Cu-O layer has been enhanced by Fe doping. The difference in valence between Fe³⁺ and Cu²⁺ induces extra oxygen into the lattice and forms the extra oxygen defects. This Fe dopant leads to a strong localization of the electrons in the Cu-O layer. So the decrement of the concentration of the itinerant electrons results in a decline of the superconducting transition temperature.