Theory of confined high Tc superconductivity in monovalent metals

Abstract

Monovalent nontransition metals are robust Fermi liquids. They defy superconductivity even at lowest temperatures (Li is a minor exception: Tc≈0.4 mK). However, Thapa, Pandey, Ghosh and collaborators 8 have reported, from 2018, signals for transient and unstable granular superconductivity at ambient temperatures in Ag nanoparticles embedded in Au matrix. We develop a theory, where competing superconducing, CDW and SDW orders lose and get confined (go off-shell). They leave behind a robust Fermi liquid on-shell. A single half filled band crossing the Fermi level provides a number of special k-space regions for singlet stabilizing umklapp pair scattering and superconductivity stabilizing repulsive pair scattering. Carefully designed perturbations could deconfine a confined superconductivity. We suggest that electron transfer (doping) from Ag nanoparticles to Au matrix (with a higher electronegativity), quasi 2D structural reconstructions (e.g., 9R structure), electronically decoupled 2D patches and 1D segments expose confined superconductivity. Beneath a calm Fermi sea, strong supercurrents may exist in several metals.