The effect of Ni and Zn doping in Bi-2212 from tunneling measurements: The MCS model of the high-Tc superconductivity in hole-doped cuprates

Abstract

We use Ni and Zn impurities doped into Bi2Sr2CaCu2O8+x (Bi2212) to test the Magnetic polaron–Spinon (MS) model proposed earlier. We present electron-tunneling spectroscopy of pure, Ni- and Zn-doped Bi2212 single crystals below T c using a break-junction technique. We show that magnetic (Ni) and nonmagnetic (Zn) impurities doped into CuO2 planes affect both the T c and the density of states in Bi2212 but do it differently. To explain these data, we had to modify the MS model. Thus, we present a magnetic coupling between stripes (MCS) model. In the MCS model, there is only one superconductivity—a spinon superconductivity along charged stripes. The coherent state of the spinon superconductivity is established by magnons which are excited by motions of charged stripes. Thus, in the MCS model, the superconductivity has the two mechanisms: along charged stripes and perpendicular to stripes.