Charge carrier localization and metal to insulator transition in cerium substituted (Bi,Pb)-2212 superconductor

We report on the details of carrier localization and metal to insulator transition in (Bi,Pb)-2212 by substituting Ce at its Sr site (0.2 ≤ x ≤ 1.0). Structural and compositional analysis confirm good homogeneity of Ce distribution in the (Bi,Pb)-2212 matrix. The resistivity measurements show that x = 0.2 sample is a superconductor while those with x > 0.2 are insulators. Resistivity in the insulating regime (0.4 ≤ x ≤ 1.0) is analyzed using a generalized hopping approach. The increase in normal state resistivity and disorder of the samples leads to a metal to insulator transition at 0.2 < x ≤ 0.4 and the insulating phases exhibit Mott's variable range hopping phenomenon. Around the transition, a dimensional change over from two to three dimensions is observed in the variable range hopping regime. Results show that substitution reduces the carrier concentration of (Bi,Pb)-2212, leads to suppression of superconductivity and metal to insulator transition in the system by localizing the electronic states at the Fermi level.