Spatial correlation between impurity states and energy gap distribution in Bi2Sr2Ca(Cu1-xZnx)2 O8+δ(x = 0.02)

We have performed scanning tunneling spectroscopy (STS) measurements on slightly over doped Bi2Sr2Ca(Cu1-xZnx)2O8+δ(x = 0.02) to investigate spatial correlation between the impurity stats and the local gap value. In addition to several impurity states, the spatial variation of energy gap has been observed. The gap values are spatially distributed from 20 meV to 55 meV with the length scale of about 5 nm. The impurity states appear only in the regions whose gap values are less than 50 meV. Furthermore, the number of Zn impurity states estimated from STS results is slightly less than that of doped Zn atoms estimated by inductively-coupled-plasma-mass-spectroscopy. Our results insist that there exist the impurity sites without the resonant states and those impurities are located on the region with the gap value of more than 50 meV.