Enhancing superconductivity via engineered polaronic environment (2408.03288v3)

Abstract: A vanishing dielectric function is required for longitudinal plasmonic or polaronic modes in a polarizable uniform medium and, in general, heralds the presence of singular charge fluctuations. It is also known that a vanishing dielectric function of an environment strengthens Cooper pairing in a superconductor via resonant anti-shielding (RAS), regardless of pairing origin. We combine these ideas in a strategy to strongly enhance superconductivity. Specifically, we propose a superlattice in which a unit cell consists of an ultrathin superconductor film in direct contact with a monolayer of a metal-organic framework material. This structure possesses a momentum-independent and resonant effective dielectric function, a key feature for RAS-enhanced superconductivity. We show that the superlattice facilitates near perfect volumetric intermixing between the superconductor and the engineered dielectric environment. To estimate the critical temperature $T_c$ enhancement, we use the unrestricted Leuven's scaling method, which relates the spectral integral of the RAS-renormalized Eliashberg function $\alpha^2$F to $T_c$, which we showed previously to be in excellent agreement with ab initio simulations, and which we posit may underlie recent observations of enhanced $T_c$ in FeSe on SrTiO$3$. We carried out a renormalization of the bare $\alpha^2$F, dividing it directly by |$\epsilon{DE} (\omega)|^2$, where $\epsilon_{DE} (\omega)$ is the q-independent dielectric function of the dielectric environment. Our estimates show that ambient temperature and pressure operation could be achievable in the RAS scheme. We also calculated the quantum Fisher information from the dynamic charge susceptibility in the normal state (for vanishing losses) in our proposed superlattice, and our estimate suggests the presence of superconductivity signatures well above $T_c$ due to quantum charge entanglement buildup.