Quadrupole-Strain Interaction in Rare Earth Hexaborides

Abstract

Temperature dependence of the elastic constants in a series of rare earth hexaborides has been investigated by means of the ultrasonic method. The remarkable softening of the transverse C 44 mode in PrB 6 , NdB 6 , DyB 6 and HoB 6 has been discussed in connection with the cooperative Jahn-Teller effect due to the CEF ground state degenerated by the quadrupolar moment. The low temperature behavior of C 44 in Ce x La 1- x B 6 compounds is presented to show the Kondo effect on the quadrupolar moment of Γ 8 ground state. The anomaly of the bulk modulus C B in SmB 6 is related to the valence fluctuation state in the system.