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

Abstract

The metamaterial approach to dielectric response engineering for enhancing the transition temperature, ${T}_{c}$, of a superconductor has been demonstrated in several recent reports. One example of this effect is ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ coated aluminum nanoparticles that form an epsilon near zero (ENZ) core-shell metamaterial superconductor with a ${T}_{c}$ that is nearly three times that of pure aluminum. Since the ${T}_{c}$ 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 ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ coated aluminum nanoparticle composite pellets with an enhanced ${T}_{c}$ that demonstrate that the Debye temperature and DOS are similar to that of pure aluminum indicating that the source of the ${T}_{c}$ enhancement is indeed a modification of the attractive electron-electron interaction.