Scanning tunneling microscopy and spectroscopy study of 4ax4a electronic charge order and the inhomogeneous pairing gap in superconducting Bi2Sr2CaCu2O8+δ

We performed scanning tunneling microscopy and scanning tunneling spectroscopy (STS) measurements on underdoped Bi2212 crystals with doping levels p similar to 0.11, similar to 0.13, and similar to 0.14 to examine the nature of the nondispersive 4ax4a charge order in the superconducting state at T < T-c. The charge order appears conspicuously within the pairing gap, and low doping tends to favor the charge order. We point out the possibility that the 4ax4a charge order will be dynamical in itself, and pinned down over regions with effective pinning centers. The pinned 4ax4a charge order is closely related to the spatially inhomogeneous pairing gap structure, which has often been reported in STS measurements on high-T-c cuprates.