Relationship between crystal chemistry and the local structure and electronic properties of Tl2Ba2Ca2Cu3O10 superconductors determined by scanning tunneling microscopy and spectroscopy.

Abstract

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) have been used to characterize the local structure and electronic properties of ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{10}$ single crystals prepared from 4:1:3:6 and 4:1:3:10 stoichiometry melts. Magnetic-susceptibility, resistivity, x-ray-fluorescence, and x-ray-diffraction measurements indicate that samples prepared from the 4:1:3:6 melts (type 1) have a chemical inhomogeneity, while crystals obtained from the 4:1:3:10 melts (type 2) are high quality. STM studies of the type-1 crystals demonstrate that the inhomogeneities can be associated with distortions in the TlO layer atomic structure. STS measurements on the distorted TlO layer of the type-1 samples have shown that this layer is also metallic. STM and STS investigations of the type-2 samples have shown, however, that the TlO layer in these crystals is tetragonal and semiconducting. In addition, a superstructure that is localized over small regions of the TlO surface has been characterized in the type-1 crystals. These results demonstrate that single crystals of the same average structure and composition can exhibit substantial differences in the local-structure electronic states and superconducting properties.