Polarization catastrophe in doped cuprates and metal-ammonia solutions: an analogy

TL;DR

This paper proposes that a polarization catastrophe caused by unscreened Coulomb interactions of bound states in doped polar dielectrics drives the metal-insulator transition, potentially explaining superconductivity and phase separation.

Contribution

It introduces the idea that a polarization catastrophe underlies the MIT in doped polar materials, linking phenomena in cuprates and metal-ammonia solutions.

Findings

Negative static dielectric constant indicates polarization catastrophe.

Polarization effects may trigger superconductivity in cuprates.

Phase separation in metal-ammonia solutions linked to polarization instability.

Abstract

On doping polar dielectrics, such as the cuprates or liquid ammonia, the long range polarization leads to the formation of bound states (polarons or solvated electrons). However, the exact role of such entities in the metal-insulator transition (MIT) still remains unclear. We suggest that the driving mechanism of the MIT is a polarization catastrophe that occurs due to their unscreened Coulomb interaction. This phenomenon is associated to a negative static dielectric constant, which could be the origin of both the superconducting transition in the cuprates -- where the doping ions are frozen in the lattice structure -- and the phase separation observed in liquid metal-ammonia solutions -- where the counter-ions are mobile.