Ultrasonic attenuation measurement on the Kondo behavior of CeCu 6

The heavy fermion compound CeCu₆ demonstrates typical Kondo behavior at low temperatures. Ultrasonic attenuation measurements performed on a CeCu₆ single crystal with frequencies up to 800 MHz over a temperature range from 200 K to 0.5 K are presented. As the temperature was lowered to about 20 K, the attenuation decreased monotonically. However, at temperatures between 2 K to 10 K, the attenuation exhibited a well defined absorption peak. As the temperature was lowered below about 2 K, the attenuation increased monotonically. The amplitude of the absorption peak was proportional to the frequency and the peak moved to higher temperatures when the frequency was increased. This absorption peak can be well fitted by α~ω ²τ/(1+ω²τ²), from which an inverse power law temperature dependence of the relaxation time τ is obtained. It is concluded that crystalline electric fields developed at low temperatures may be responsible for the absorption peak