Emergent superconductivity in doped ferroelectric hafnia

Abstract

Superconductivity and ferroelectricity,representing two distinct forms of ordered states, are typically not found together in the same system, making it even more difficult to create a connection between them. Here, supported by first-principles calculations, we propose that Anderson-Blount's ferroelectric-like metal can be manifested in electron-doped ferroelectric Pca2$_1$ HfO$_2$. In this system, polar phonons and consequently ferroelectricity are not affected by the presence of itinerant electrons. We find that a nonpolar optical phonon, being strongly coupled to doped electrons, can acquire a pronounced electron-phonon coupling strength to activate conventional Bardeen-Cooper-Schrieffer superconductivity. The displacements of polar oxygen atoms in Pca2$_1$ HfO$_2$ create a link between ferroelectricity and superconductivity, enabling a tunable superconducting temperature ranging approximately from 10 to 30 Kelvin. Owing to hafnia's compatibility with silicon, we suggest HfO$_2$-based ferroelectric superconductors present an opportunity to construct high-performing hybrid integrated systems utilizing switchable quantum states.