STM/STS Study on 4a × 4a Electronic Charge Modulation of Bi2Sr2CaCu2O8+δ

We performed low‐bias STM measurements on lightly doped Bi2212 crystals, and confirmed the development of two‐dimensional (2D) superstructure with a periodicity of four lattice constants (4a) within the Cu‐O layer at T < TC. This 4a × 4a superstructure orients along the Cu‐O bonding direction, and is nondispersive. The nondispersive 4a × 4a superstructure was clearly observed within the ZTPG or d‐wave gap, while it tended to fade out outside the gaps.