Anisotropy of Electronic Structure and Transport Properties of Oxide Superconductors

Extract

High temperature superconductivity in cuprates has become a fairly mature field now that more than a decade has passed by since its discovery. While scientific appeal of the field continues, the technological implications have faced harsh realities. Although the transition temperatures are high, the coherence length in oxide superconductors is awfully short and thus inhomegeneity or perturbation at the length scale of a few nanometers proves extremely detrimental to their properties, especially transport. Further, slight changes in the oxygen stoichiometry in cuprates have a profound effect on their superconducting properties and it is often not clear whether the nonstoichiometry at defect sites (e.g. grain boundaries- GBs) is intrinsic or extrinsic.

The anisotropy of electronic structure is well reflected in low loss EELS spectra of these materials. Figure 1 shows low loss EELS spectra from Y124: one taken with momentum transfer confined to the Cu-02 planes, and the other normal to them. These observations are in accord with the fact that conduction is predominantly along the ab-planes, within single crystals.