Site-selective Mott transition in rare earth nickelates

TL;DR

This paper demonstrates that the metal-insulator transition in rare earth nickelates is due to a site-selective Mott phase, where localized and itinerant electrons coexist, explaining key experimental features and suggesting broader applicability.

Contribution

It introduces the concept of a site-selective Mott transition in nickelates, combining DFT and DMFT calculations to explain their unique electronic and magnetic properties.

Findings

Reproduces insulating gap and magnetic moment variation

Shows absence of charge order in nickelates

Links structural features to insulating behavior

Abstract

A combination of density functional and dynamical mean field theory calculations are used to show that the remarkable metal-insulator transition in the rare earth nickelate perovskites arise from a site-selective Mott phase, in which the $d$-electrons on a half of the Ni ions are localized to form a fluctuating moment while the $d$-electrons on other Ni ions form a singlet with holes on the surrounding oxygen ions. The calculation reproduces key features observed in the nickelate materials, including an insulating gap in the paramagnetic state, a strong variation of static magnetic moments among Ni sites and an absence of "charge order". A connection between structure and insulating behavior is documented. The site-selective Mott transition may be a more broadly applicable concept in the description of correlated materials.