Atomic-scale spot structures and gap distributions on apical-fluorine cuprate superconductor Ba2Ca5Cu6O12 (O1−x, Fx)2 observed by STM/STS

The atomic-scale surface electronic states on the multi-layered apical-fluorine cuprate superconductor Ba2Ca5Cu6O12 (O1−x, Fx)2 (Tc ≃ 70K) are investigated by using low temperature scanning tunneling microscopy/spectroscopy (STM/STS). The spatial gap distributions show the patch scale of ∼ 0.5 nm, which is quite shorter than the superconducting coherence length ∼ 2-3 nm of other cuprate superconducters of a few nm. The high-bias (∼ 1V) conductance map contains some characteristic spots with contrasts reverse to those at low bias, which are considered to be due to the charge unbalance of apical atoms such as O2− and F−.This research was supported by Grant-in-Aid for Scientific Research (No. 19540370) from JSPS, Japan