Bound state of 4f-excitation and magnetic resonance in unconventional superconductors
Abstract
We analyze the influence of unconventional superconductivity on crystalline electric field (CEF) excitations of rare earth ions in novel superconductors. We show that resonant magnetic excitations of the conduction electrons that have been observed in these systems below Tc may result in the formation of the bound state in the 4f-electron susceptibility. This occurs at energies well below the CEF excitation energy. The effect is discussed as a function of temperature and the strength of the coupling between the 4f and d-electrons. We argue that these effects may be present in the layered cuprates and ferropnictides which contain rare-earth ions.
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