Electron-phonon mediated superconductivity in La$_6$Ni$_5$O$_{12}$ nickel oxides

TL;DR

This study investigates La$_6$Ni$_5$O$_{12}$ nickel oxides, revealing charge and bond ordered phases that can mediate superconductivity through phonons, with a predicted critical temperature aligning with experimental observations.

Contribution

The paper demonstrates that phonons in La$_6$Ni$_5$O$_{12}$ can mediate superconductivity, providing insights into the pairing mechanism in nickel oxide superconductors.

Findings

Charge and bond ordered insulating phases exist in the phase diagram.

Doping quenches insulating phases, leading to metallic behavior.

Phonons in the material can mediate Cooper pairing with T$_c$ between 11-19K.

Abstract

Nickel oxide superconductors offer an alternative playground for understanding the formation of Cooper pairs in correlated materials such as the famous cuprates. By studying the La$_{n+1}$Ni$_n$O$_{2n+2}$ phase diagram on the basis of hybrid and spin-polarized density functional theory simulations, we reveal the existence of charge and bond ordered (CBO) insulating phases that are quenched by doping effects, ultimately resulting in a metallic phase at the n=5 member. Nevertheless, the phonons associated with the CBO identified in the phase diagram remain sufficiently large to mediate Cooper pairs in La$_6$Ni$_5$O$_{12}$, yielding a computed critical temperature between T$_c$=11-19K consistent with the 13K observed experimentally in Nd$_6$Ni$_5$O$_{12}$. Thus, in order to identify the superconducting mechanism, extracting the relevant instabilities in the doping phase diagram of superconductors appears critical.