Disorder and coherence in heavy-fermion systems

The effects of disorder on the formation of the coherent state in heavy-fermion systems are studied. The renormalized heavy band, characterized by an effective hybridization parameter, is destabilized by a critical strength of impurity scattering leading to self-energy corrections of order $T_K$. For a higher degree of disorder the heavy-fermion system will behave much like a collection of independent Kondo impurities, lacking the characteristic signatures of coherence in resistivity, specific heat, etc. The substitution of impurities on the conduction-electron side has a little influence on coherence; most of the effect comes from the strength of impurity scattering on the f-electron sites. The results are discussed in connection with experimental data.