Observation of plasmon-phonons in a metamaterial superconductor using inelastic neutron scattering

A metamaterial approach is capable of drastically increasing the critical temperature, $T_c$ , of composite metal-dielectric superconductors as demonstrated by the tripling of $T_c$ that was observed in bulk Al-Al₂O₃ coreshell metamaterials. A theoretical model based on the Maxwell-Garnett approximation provides a microscopic explanation of this effect in terms of electron-electron pairing mediated by a hybrid plasmon-phonon excitation. We report an observation of this excitation in Al-Al₂O₃ core-shell metamaterials using inelastic neutron scattering. This result provides support for this mechanism of superconductivity in metamaterials.