Thermal conductivity of the YbMgCu4 “light” heavy-fermion system

The thermal conductivity and electrical resistivity of a sample of YbMgCu4 belonging to “light” heavy-fermion compounds have been measured in the temperature range 5–300 K. The sample studied was in the region of homogeneity of this compound. It is shown that, throughout the temperature range studied, the phonon thermal conductivity of the sample has an amorphous-like character, which should be assigned to the homogeneous mixed valence of the Yb ion in YbMgCu4.