Atomic-scale images of charge ordering in a mixed-valence manganite

TL;DR

This paper presents the first atomic-scale images of charge ordering and phase separation in a transition metal oxide, revealing correlations with structural order and local electronic properties, advancing understanding of manganite phenomena.

Contribution

It introduces a novel STM-based method to directly image charge ordering and phase separation at atomic resolution in a manganite.

Findings

Charge order correlates with structural order.

Charge order links to local metallic or insulating states.

First atomic-scale images of charge ordering in a transition metal oxide.

Abstract

Transition-metal perovskite oxides exhibit a wide range of extraordinary but imperfectly understood phenomena. Charge, spin, orbital, and lattice degrees of freedom all undergo order-disorder transitions in regimes not far from where the best-known of these phenomena, namely high-temperature superconductivity of the copper oxides, and the 'colossal' magnetoresistance of the manganese oxides, occur. Mostly diffraction techniques, sensitive either to the spin or the ionic core, have been used to measure the order. Unfortunately, because they are only weakly sensitive to valence electrons and yield superposition of signals from distinct mesoscopic phases, they cannot directly image mesoscopic phase coexistence and charge ordering, two key features of the manganites. Here we describe the first experiment to image charge ordering and phase separation in real space with atomic-scale resolution in a transition metal oxide. Our scanning tunneling microscopy (STM) data show that charge order is correlated with structural order, as well as with whether the material is locally metallic or insulating, thus giving an atomic-scale basis for descriptions of the manganites as mixtures of electronically and structurally distinct phases.