Striped nanoscale phase separation at the metal-insulator transition of heteroepitaxial nickelates

TL;DR

This study uses microscopy to reveal how nanoscale striped insulating domains form and grow during the metal-insulator transition in heteroepitaxial NdNiO3 films, influenced by surface morphology and stable across cycles.

Contribution

It uncovers the nanoscale striped phase separation pattern and the role of surface morphology in the MIT of heteroepitaxial nickelates, providing new insights into their phase transition mechanisms.

Findings

Striped insulating domains form along terraces of atomically flat surfaces.

Transition temperature distribution is intrinsic and stable across cycles.

Heteroepitaxy influences the nanoscale phase separation pattern.

Abstract

Nucleation processes of mixed-phase states are an intrinsic characteristic of first-order phase transitions, typically related to local symmetry breaking. Direct observation of emerging mixed-phase regions in materials showing a first-order metal-insulator transition (MIT) offers unique opportunities to uncover their driving mechanism. Using photoemission electron microscopy, we image the nanoscale formation and growth of insulating domains across the temperature-driven MIT in NdNiO3 epitaxial thin films. Heteroepitaxy is found to strongly determine the nanoscale nature of the phase transition, inducing preferential formation of striped domains along the terraces of atomically flat stepped surfaces. We show that the distribution of transition temperatures is an intrinsic local property, set by surface morphology and stable across multiple temperature cycles. Our data provides new insights into the MIT of heteroepitaxial nickelates and points to a rich, nanoscale phenomenology in this strongly correlated material.