Local density of states (LDOS) and the lattice structure of highly underdoped Bi2Sr2CaCu2O8+ δ with Tc = 22 K and 30 K were investigated by a low temperature scanning tunneling microscope. The modulation structure of the Bi-O surface was strongly depressed in the highly underdoped samples. The depression was observed only in the samples subject to the strong reduction annealing process, suggesting that the strong reduction in excess oxygen could destroy the modulation structure. At a time, patch-like inhomogeneity in the gap map sometimes disappeared, indicating that the existence of excess oxygen has an important role in the patch formation. Analysis on the LDOS with various doping levels showed that there was no crossover energy, which separates a pseudogap and a superconducting gap and is proportional to Tc.
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