Observation of Plasmon-Phonons in a Metamaterial Superconductor using Inelastic Neutron Scattering
Vera N. Smolyaninova, Jeffrey W. Lynn, Nicholas P. Butch, Huaiyu H Chen-Mayer, Joseph C. Prestigiacomo, M. S. Osofsky, Igor I. Smolyaninov
Recent experiments have demonstrated that the metamaterial approach is capable of drastically increasing the critical temperature, Tc, of composite metal-dielectric epsilon near zero (ENZ) metamaterial superconductors. For example, a tripling of the critical temperature has been observed in Al-Al2O3 ENZ core-shell metamaterials. A theoretical model based on the Maxwell-Garnett effective medium approximation provides a microscopic explanation of this effect in terms of electron-electron pairing mediated by a hybrid plasmon-phonon excitation in the composite metal-dielectric metamaterial. We report the first observation of a hybrid plasmon-phonon excitation in Al-Al2O3 ENZ core-shell metamaterials using inelastic neutron scattering. These results provide strong support for this novel mechanism of superconductivity in ENZ metamaterials.