EFFECTIVE DIMENSIONALITY OF CUPRATE SUPERCONDUCTORS

A novel optical method for accurate monitoring of the carrier density N in layered conductors is introduced. It is applied to several cuprate superconductors, and it is found that T(c) does not scale with N. However, if the closely spaced pairs or triplets of CuO2 planes were coupled together to act as distinct metallic slabs, the relevant variable could be n, the slab carrier density. Indeed, we found that T(c) does scale nicely with n. This suggests that high-T(c) superconductivity is effectively a two-dimensional phenomenon; it can occur in a cuprate slab which is only one unit cell thick. Finally, estimates are obtained for the length scales of localization of charge carriers: d almost-equal-to 8 angstrom and d perpendicular-to less-than-or-similar-to 2 angstrom in all the cuprates under study.