After annealing to 20 K, the logarithm of the resistivity (ln R) was found to follow a $ T^{-1/4} $ dependence. These films did not exhibit superconductivity even at the lowest attainable temperatures (T ~ 1.5 K). The behavior suggests a metal-nonmetal transition in the Hg-Xe system, dependent on concentration and approaching the critical concentration of continuous percolation in 3D. Beyond percolation, the system has a negative temperature coefficient of resistance (TCR) but remains superconducting. At higher Xe concentrations, hopping-dominated conductivity is observed. The transition to an insulating state beyond percolation is likely the Mott-Anderson transition, accompanied by the disappearance of superconductivity. The authors thank R. Mikkelson for discussions and acknowledge support from the U.S. Department of Energy. The study of CeCu₂Si₂ reveals superconductivity in a metal with strongly renormalized conduction-electron properties due to many-body interactions. Unlike LaCu₂Si₂, which behaves as a normal metal, CeCu₂Si₂ exhibits low-temperature anomalies typical of "unstable 4f shell" behavior and transitions into a superconducting state at Tc ~ 0.5 K. The superconductivity is attributed to a novel state, with the Meissner effect observed. The specific heat and resistivity data indicate a second-order phase transition, with a spin-fluctuation temperature T* ~ 10 K. The superconductivity is intrinsic, not due to impurities, and the critical field shows type-II behavior. The study concludes that CeCu₂Si₂ is an intrinsic superconductor, with a specific heat jump consistent with BCS theory. The results suggest it behaves as a "high-temperature superconductor" and cannot be described by conventional superconductivity theory. The work was supported by the Deutsche Forschungsgemeinschaft.After annealing to 20 K, the logarithm of the resistivity (ln R) was found to follow a $ T^{-1/4} $ dependence. These films did not exhibit superconductivity even at the lowest attainable temperatures (T ~ 1.5 K). The behavior suggests a metal-nonmetal transition in the Hg-Xe system, dependent on concentration and approaching the critical concentration of continuous percolation in 3D. Beyond percolation, the system has a negative temperature coefficient of resistance (TCR) but remains superconducting. At higher Xe concentrations, hopping-dominated conductivity is observed. The transition to an insulating state beyond percolation is likely the Mott-Anderson transition, accompanied by the disappearance of superconductivity. The authors thank R. Mikkelson for discussions and acknowledge support from the U.S. Department of Energy. The study of CeCu₂Si₂ reveals superconductivity in a metal with strongly renormalized conduction-electron properties due to many-body interactions. Unlike LaCu₂Si₂, which behaves as a normal metal, CeCu₂Si₂ exhibits low-temperature anomalies typical of "unstable 4f shell" behavior and transitions into a superconducting state at Tc ~ 0.5 K. The superconductivity is attributed to a novel state, with the Meissner effect observed. The specific heat and resistivity data indicate a second-order phase transition, with a spin-fluctuation temperature T* ~ 10 K. The superconductivity is intrinsic, not due to impurities, and the critical field shows type-II behavior. The study concludes that CeCu₂Si₂ is an intrinsic superconductor, with a specific heat jump consistent with BCS theory. The results suggest it behaves as a "high-temperature superconductor" and cannot be described by conventional superconductivity theory. The work was supported by the Deutsche Forschungsgemeinschaft.