Giant lattice softening in the normal state of CeRu 2

Abstract

Elastic moduli of high-quality single-crystalline CeRu 2 have been measured between 2 and 300 K by an ultrasonic technique. Both shear moduli of ( C 11 − C 12)/2 and C 44 show a giant softening without structural transition. In contrast to the shear moduli, the bulk modulus C B indicates a normal temperature dependence without the anomalous softening. These results reveal that there exists a remarkable structural fluctuation corresponding to shearing strain in the normal state of CeRu 2. The analysis taking account of the deformation potential coupling between the strain and an electronic energy band demonstrates that degenerate and peaked density of states is responsible for the softening.