Surface structure of Bi2Sr2CaCu2O8+δ high-temperature superconductors studied using low-energy electron diffraction

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Abstract
The surface structure of Bi2Sr2CaCu2O8+δ has been studied using low‐energy electron diffraction (LEED). Sharp diffraction spots indicative of a well‐ordered surface are observed. The LEED patterns unequivocally show that this type of material preferentially cleaves along the a‐b planes of the nearly tetragonal unit cell. A superstructure extending along one of the axes in the a‐b plane (b) is found to have a periodicity of 27±0.5 Å, in good agreement with earlier studies of the three‐dimensional crystal structure. We conclude that the superstructure at the surface is nonlocal in character and reflects the long‐range superlattice of the bulk along the b axis. Intensity modulations of the diffraction spots oriented along the b axis are also reported and discussed in terms of the cell dimension of the unit cell along the b axis.