Metallic Bilayers: A Controlled Microscopic Theory and Critical Re-examination

The following article takes a recent proposal – that a moiré superlattice of two metallic sheets could enhance superconductivity to room temperature via artificially soft phonons – and casts it into a rigorously formulated microscopic model. I derive explicit, parametrized estimates, compute the superconducting transition temperature Tc using strong-coupling theory, and compare with both historical soft-phonon superconductors and recent moiré flat-band systems. A crucial finding is that the naive claim of Tc≈280K for a 4 meV average phonon energy is numerically inconsistent with the very same Allen–Dynes formula employed; the maximum Tc achievable with such soft modes is below 30 K. I therefore present a corrected, realistic scenario in which moiré engineering raises Tc of a simple metal (Pb or NbSe₂) from ~7 K to 20–25 K, while I discuss in detail the limits of validity of Eliashberg theory. This work serves as a prudent roadmap for an experiment that is fully realisable with 2026 fabrication capabilities. I emphasize that both the electronic enhancement and the phonon softening discussed here rely on conditions that are sensitive to sample quality and dimensional confinement, and should therefore be regarded as tunable rather than universal features of twisted metallic bilayers.