Bound state of 4$f$-excitation and magnetic resonance in unconventional superconductors

TL;DR

This paper investigates how unconventional superconductivity affects 4f-electron excitations, revealing possible bound states formed due to magnetic resonances in certain high-temperature superconductors.

Contribution

It demonstrates that magnetic resonances in superconductors can induce bound states in 4f-electron susceptibility, a novel insight into electron interactions in these materials.

Findings

Bound states form below CEF excitation energies.

Effects depend on temperature and electron coupling strength.

Potential presence in cuprates and ferropnictides.

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 T$_c$ may result in the formation of the bound state in the 4$f$-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 4$f$ and $d$-electrons. We argue that these effects may be present in the layered cuprates and ferropnictides which contain rare-earth ions.