Bending and breaking of stripes in a charge ordered manganite

Benjamin H Savitzky,Alemayehu S Admasu,Ismail El Baggari,Sang-Wook Cheong,Robert Hovden,Jaewook Kim,Lena F Kourkoutis

doi:10.1038/s41467-017-02156-1

Abstract

In charge-ordered phases, broken translational symmetry emerges from couplings between charge, spin, lattice, or orbital degrees of freedom, giving rise to remarkable phenomena such as colossal magnetoresistance and metal–insulator transitions. The role of the lattice in charge-ordered states remains particularly enigmatic, soliciting characterization of the microscopic lattice behavior. Here we directly map picometer scale periodic lattice displacements at individual atomic columns in the room temperature charge-ordered manganite Bi0.35Sr0.18Ca0.47MnO3 using aberration-corrected scanning transmission electron microscopy. We measure transverse, displacive lattice modulations of the cations, distinct from existing manganite charge-order models. We reveal locally unidirectional striped domains as small as ~5 nm, despite apparent bidirectionality over larger length scales. Further, we observe a direct link between disorder in one lattice modulation, in the form of dislocations and shear deformations, and nascent order in the perpendicular modulation. By examining the defects and symmetries of periodic lattice displacements near the charge ordering phase transition, we directly visualize the local competition underpinning spatial heterogeneity in a complex oxide.

Highlights

In charge-ordered phases, broken translational symmetry emerges from couplings between charge, spin, lattice, or orbital degrees of freedom, giving rise to remarkable phenomena such as colossal magnetoresistance and metal–insulator transitions
Striped states have been imaged in manganites with dark-field transmission electron microscopy (DF-TEM), resolution and signal-to-noise are limited in DF-TEM because electrons are collected from a small window of momentum space[13,14]
We find two coexisting periodic lattice displacements (PLDs), forming locally unidirectional domains as small as ~5 nm despite appearing bidirectional over larger length scales, a distinction which is important but often challenging to establish[10,14,20,21]

Summary

Introduction

In charge-ordered phases, broken translational symmetry emerges from couplings between charge, spin, lattice, or orbital degrees of freedom, giving rise to remarkable phenomena such as colossal magnetoresistance and metal–insulator transitions. We directly map picometer scale periodic lattice displacements at individual atomic columns in the room temperature charge-ordered manganite Bi0.35Sr0.18Ca0.47MnO3 using aberration-corrected scanning transmission electron microscopy. By examining the defects and symmetries of periodic lattice displacements near the charge ordering phase transition, we directly visualize the local competition underpinning spatial heterogeneity in a complex oxide. Charge density wave (CDW) states are periodic modulations of both the electron density and atomic lattice positions. These states epitomize emergent order via electron–lattice interaction, and have taken a central role in understanding exotic phenomena in complex materials. We quantitatively map picometer scale (

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Results

Conclusion