Elastic behavior near the metal-insulator transition of (formula presented)

Abstract

We report on temperature-dependent sound velocity measurements of surface acoustic waves performed on small (Formula presented) single crystals by means of ultrasonic microscopy. The elastic behavior of this compound has been studied ultrasonically through its metal-insulator transition. The investigations reveal a strong elastic anisotropy in the metallic phase which is reminiscent of the insulator (Formula presented) Surprisingly, the anisotropy disappears almost completely, when the insulating phase is developed. The accompanying changes in lattice entropy are large and suggest that there is less reason to favor electron-electron correlations as a driving force of the metal-insulator transition in (Formula presented) © 1999 The American Physical Society.