ELASTIC PROPERTIES OF THE HEAVY-FERMION SUPERCONDUCTOR URU2SI2

Measurements of the elastic constants in the normal and superconductin g state on a high quality URu2Si2 single crystal exhibit large anomali es in the c11 mode versus temperature around 30 K and T(c). No such an omalies are visible in the c33 mode and in the shear elastic constants . We describe this behaviour with the anisotropic Gruneisen parameter coupling. Using the c11 anomaly a B-T phase diagram is determined whic h clearly shows the single phase bulk properties of superconducting UR U2Si2. The magnetic field dependences of the shear waves in the superc onducting and normal state can be interpreted quantitatively with a Lo rentz force mechanism.