Nanodomain structure and function of high-temperature superconductors

The causes of high-temperature superconductivity are still mysterious, although more than 50000 experiments have studied this subject. The most severe test of any microscopic theory is generally considered to be its ability to predict the results of future experiments. Here we examine recent (1999-2001) studies of Bi2Sr2CaCu2O8+δ films by scanning tunnelling microscopy; these have revealed a nanodomain structure on a scale of 3 nm, which is closely correlated with both superconductive gaps and pseudogaps. This structure and these correlations were predicted as part of a discrete filamentary model of high-temperature superconductivity in 1990. The nanodomain diameter of 3 nm was identified in experiments on YBa2Cu3O7 in 1996. While none of the experiments can directly establish causes, in the predictive theoretical model it was proposed that the underlying forces generating the nanostructure are ferroelastic. It was also predicted that the strong correlations of the superconductive gap and pseudogap electronic structure with nanostructure are the result of dopant self-organization. Here we describe a new method of preparing boride alloys, and we predict that it may produce materials with Tc approximately equals 150 K or more.