Electron polaron effects in heavy-electron systems

Heavy-electron materials exhibit Fermi-liquid behavior at low temperatures and single-site spin-fluctuation behavior at high temperatures. There is strong experimental evidence that the fermion excitations at low temperatures are itinerant f electrons. It is shown in this paper that the Coulomb correlation between an f hole and the conduction-band electrons causes the f electrons to propagate like small polarons in insulators and semiconductors, and the accompanying screening cloud is formed by broadband electrons. At elevated temperatures the polaron is increasingly attenuated that it gradually becomes localized. This mechanism may explain many anomalous properties of heavy-electron materials up to the crossover temperature, suggesting that the crossover could be driven by the polaron effect.