Is there an ideal phase diagram for high-temperature superconductors?

Abstract

Powerful new/old experimental evidence supports the filamentary model, for the metal-insulator transition in randomly doped, uncompensated impurity-band semiconductors. The resulting phase diagram, which contains an intermediate ‘X’ phase, closely resembles the usual phase diagram for high-temperature superconductors, leading to the identification of the X phase (which is often called a ‘non-Fernii liquid’) as an anisotropic 3d filamentary metal. An important by-product of the new/old evidence is that it leads to a quantitative, parameter-free estimate of the strength of the dopant electron-ion interaction energies, which in the impurity band case are 25 times larger than those of bonding valence electrons, corresponding to a maximum T _c ∼ 150 K. A phase diagram is predicted for an ‘ideal’ high-temperature superconductor which is characteristically different from that currently sketched in experimental papers; observation of such a phase diagram would constitute strong evidence in favour of the filamentary model.