Structural Instability, Anharmonicity, and High-Temperature Superconductivity in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi><mml:mo>−</mml:mo><mml:mn>15</mml:mn></mml:math>-Structure Compounds

Abstract

The strain dependence of ${T}_{c}$ inferred from velocity of sound data, is given for a number of $A\ensuremath{-}15$-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.