Disorder effects in cuprates

We report on ah-plane resistivity (rho) and angle-reserved photoemission (ARPES) spectra for Bi2Sr2CaCu2O8+x single crystals irradiated with neutrons or electron-beam irradiation. Both the normal and superconducting states were measured with angle-resolved photoemission. Electron-beam irradiation leads to an increase in the residual resistivity, and a decrease in the superconducting transition temperature (T-c). The resistivity data does not indicate any pseudogap; the resistivity is linear from T-c to 300K for all levels of disorder, and the slope (d rho /dT) is the same for all levels of disorder. The superconducting state ARPES data exhibits no change in the binding energy of the "peak" for Brillouin zone locations near the (0, pi) point. The peak spectral intensity decreases with increasing disorder, the gap fills in, but the peak neither shifts nor broadens. The normal state exhibits a pseudogap developing with disorder; the size of the pseudogap increases as the residual resistivity increases. The pseudogap is anisotropic, largest near the (0, pi) point and zero in the direction. Neutron-beam irradiation causes an increase in the residual resistivity. The resistivity data exhibit a change of slope and indications of a pseudogap for neutron irradiation. For normal state ARPES data of neutron-beam irradiated samples, there is also an anisotropic pseudogap; it is also zero in the direction and large near the (0, pi) point. We discuss implications of these data.