The effect of deliberately induced disorder on the electronic structure of the Bi-2212 high T-c superconductor

We have irradiated by thermal neutrons single crystals of the Bi-2212 high T-c superconductor. The irradiated samples are insulators, but they regain high T-c superconductivity after an annealing in He at 450-550 degrees C. Depending on irradiation doses and annealing parameters, we obtained two insulators, with more or less disorder, and two superconductors with different values of T-c. We performed resistivity, a.c. susceptibility and angle resolved photoemission studies (ARPES). The coherent quasiparticle intensity in the vicinity of the chemical potential is considerably reduced in the insulating samples along both the Gamma-M and Gamma-Y high symmetry directions. It is recovered once the superconductivity is reestablished, and develops together with T-c along the Cu-O bond (Gamma-M) direction.