Charge ordering, stripes and phase separation in manganese perovskite oxides: an STM/STS study

TL;DR

This study uses STM/STS to analyze charge ordering, phase separation, and structural changes in manganese perovskite oxides, revealing atomic-scale phase coexistence and correlations with electronic states during the metal-insulator transition.

Contribution

It provides detailed atomic-scale insights into charge ordering and phase coexistence in BCMO, advancing understanding of CMR mechanisms.

Findings

Charge ordering correlates with local conduction and structural order.

Distinct atomic phases are observed above and below the MIT.

Coexistence of phases indicates a first order phase transition.

Abstract

A microscopic characterisation of the phase transitions associated with colossal magnetoresistance (CMR) in manganese perovskite oxides is a very important ingredient in the quest of understanding its underlying mechanism. Scanning tunneling microscopy (STM) is most suitable to investigate some of their reported hallmarks, including charge ordering, lattice distortions, and electronic phase separation. Here we investigate Bi1-XCaXMnO3 (BCMO) with x=0.76. At this composition, BCMO develops an insulating charge-ordered phase upon cooling, whose study as a function of temperature will allow identifying atomic scale characteristics of the metal-insulator phase transition (MIT). We observe distinct atomic scale phases at temperatures above and below the MIT, with very different electronic and structural characteristics. Combining STM micrographs and current-voltage tunneling characteristics, we find that charge ordering correlates both with the local conduction state (metallic or insulating) and the local structural order. Furthermore, STM shows coexistence of these phases as expected for a first order phase transition.