A common thread linking the heavy-fermion, cuprate and iron superconductors

Is the pairing interaction which is responsible for superconductivity in the heavy-fermion, cuprate and iron-pnictide materials similar or different? These materials come in families which contain quasi-2D layers of correlated d or f electrons. Their phase diagrams show antiferromagnetism or SDW phases in close proximity or coexisting with superconductivity. The ratio of their superconducting transition temperatures Tc to the Fermi energy or coherence scale is similar and large relative to that of the traditional electron-phonon superconductors. The resonant peak observed in inelastic neutron scattering experiments in the superconducting phase provides a signature for an unconventional gap. Single and multi-band Hubbard models have been found to describe a number of the observed properties of these systems. Here, based on the experimental phenomenology and studies of the momentum and frequency dependence of the pairing interaction for Hubbard-like models, we suggest that spin-fluctuation mediated pairing is the common thread linking this broad class of superconducting materials.