This review discusses the heavy-electron compounds and related materials from the perspective of their electrodynamic response. The investigation of the electrodynamic response by means of optical methods, extending over a very broad spectral range, should reveal, in principle, the complete excitation spectrum. This study incorporates several important sources of information on the intrinsic properties of the investigated materials. In particular, attention will be focused on the optical properties of prototype heavy-electron systems and on Kondo systems with low-temperature non-Fermi-liquid behavior or insulating characteristics. In the discussion, the electrodynamic response will be related to other relevant results arrived at by various experimental methods and to the theoretical state of the art.

DOI:https://doi.org/10.1103/RevModPhys.71.687