Resonant Mode in Rare-earth based Strongly Correlated Semiconductors

An extensive study of the spin dynamics in the strongly correlated semiconductors YbB12 and SmB6, as well as in the series of related electron-doped systems, has been performed by means of inelastic neutron scattering spectroscopy. It was found that rare-earth compounds with a valence instability may develop an exciton-like in-gap excitation, generally similar to the so-called resonant mode initially discovered in HTSC. The results of this work, along with the literature data for a number of high-Tc-, heavy-fermion- and pnictide superconductors and some magnetic compounds point to such type of resonant excitations being characteristic for systems with gap-like dynamical response in the presence of competing interactions. The correlation between the temperature evolutions of the resonant mode and of the gap in the excitation spectrum is discussed.