STM/STS Study on 4<i>a</i>×4<i>a</i>Electronic Charge Order of Superconducting Bi₂Sr₂CaCu₂O_8+δ

Abstract

We performed low-bias STM measurements on underdoped Bi2212 crystals, and\nconfirmed that a two-dimensional (2D) superstructure with a periodicity of four\nlattice constants (4a) is formed within the Cu-O plane at T&lt;Tc. This 4a X 4a\nsuperstructure, oriented along the Cu-O bonding direction, is nondispersive and\nmore intense in lightly doped samples with a zero temperature pseudogap (ZTPG)\nthan in samples with a d-wave gap. The nondispersive 4a X 4a superstructure was\nclearly observed within the ZTPG or d-wave gap, while it tended to fade out\noutside the gaps. The present results provide a useful test for various models\nproposed for an electronic order hidden in the underdoped region of high-Tc\ncuprates.\n