Structural Instability, Anharmonicity, and High-Temperature Superconductivity inA−15-Structure Compounds

Abstract

The strain dependence of $T_c$ inferred from velocity of sound data, is given for a number of $A-15$-structure compounds. Arguments relating the high $T_c$ and the structural instability are presented and a correlation of the corresponding strain dependences is proposed. The unusual anharmonicity expected is confirmed by old and new experimental data. A model for the superconducting and anomalous-normal-state properties, based on the anharmonicity rather than singular bare-electron properties, is presented. Several conjectures on structural instability and high-temperature superconductivity are made.