Normal state specific heat of a core-shell aluminum-alumina metamaterial composite with enhanced Tc

The metamaterial approach to dielectric response engineering for enhancing the transition temperature, Tc , of a superconductor has been demonstrated in several recent reports. One example of this effect is Al2 O3 coated aluminum nanoparticles that form an epsilon near zero (ENZ) core-shell metamaterial superconductor with a Tc that is nearly three times that of pure aluminum. Since the Tc of a conventional low temperature superconductor is determined by the Debye temperature and the coupling strength, which is expressed as the product of the single particle density of state (DOS) at the Fermi energy and an attractive electron-electron potential, it is natural to explore these properties to determine whether the attractive potential is responsible for the enhancement. In this report, we present specific heat results obtained from Al2 O3 coated aluminum nanoparticle composite pellets with an enhanced Tc that demonstrate that the Debye temperature and DOS are similar to that of pure aluminum indicating that the source of the Tc enhancement is indeed a modification of the attractive electron-electron interaction.