Elastic Soft Mode and Crystalline Field Effect of Kondo Lattice Substance; CeCu₆

Abstract

Temperature dependences of the elastic constants of the Kondo lattice substance CeCu 6 have been measured by the ultrasonic method. The transverse C 66 mode exhibits a complete softening, which is associated with the structural phase transition from the orthorhombic D 16 2h to the monoclinic C 5 2h structures at T c =168 K. The crystalline electric field effect has been observed in the softening of the elastic constants below about 100 K. The longitudinal C 11 and C 33 modes show a remarkable softening below 10 K, which is related to the excitation of the Kondo lattice.