Commensurate Stripes and Phase Coherence in Manganites Revealed with Cryogenic Scanning Transmission Electron Microscopy

TL;DR

This study uses cryogenic scanning transmission electron microscopy to reveal that incommensurate charge order in manganites is actually lattice-commensurate at the atomic level, highlighting the role of lattice coupling and phase coherence.

Contribution

It demonstrates that incommensurate diffraction signals can arise from phase inhomogeneity in a lattice-locked charge order, providing a microscopic understanding of charge order in manganites.

Findings

Charge order is lattice-commensurate at both room and cryogenic temperatures.

Phase inhomogeneity at room temperature transitions to phase coherence at 93K.

Atomic displacements indicate strong charge-lattice coupling.

Abstract

Incommensurate charge order in hole-doped oxides is intertwined with exotic phenomena such as colossal magnetoresistance, high-temperature superconductivity, and electronic nematicity. Here, we map at atomic resolution the nature of incommensurate order in a manganite using scanning transmission electron microscopy at room temperature and cryogenic temperature ($\sim$ 93K). In diffraction, the ordering wavevector changes upon cooling, a behavior typically associated with incommensurate order. However, using real space measurements, we discover that the underlying ordered state is lattice-commensurate at both temperatures. The cations undergo picometer-scale ($\sim $6-11 pm) transverse displacements, which suggests that charge-lattice coupling is strong and hence favors lattice-locked modulations. We further unearth phase inhomogeneity in the periodic lattice displacements at room temperature, and emergent phase coherence at 93K. Such local phase variations not only govern the long range correlations of the charge-ordered state, but also results in apparent shifts in the ordering wavevector. These atomically-resolved observations underscore the importance of lattice coupling and provide a microscopic explanation for putative "incommensurate" order in hole-doped oxides.