STM/STS STUDY ON LOCAL ELECTRONIC STATES OF UNDERDOPED Bi₂Sr₂CaCu₂O_8+δ

Spatial variation of low temperature tunneling spectrum on atomic scale was examined on the slightly underdoped Bi2212 sample (T_c~74K, p~0.12) by using a STM/STS technique. We observed a V-shaped gap with sharp coherence peaks, which is expected for d-wave superconductors, over the distance of ~18 nm and no other kind of gap. The spatial variation of gap size Δ₀ is small, ranging from 41 to 53 meV. These results indicate that the superconductivity takes place rather homogeneously in the slightly underdoped sample.