Key role of lattice symmetry in the metal-insulator transition of NdNiO3 films

TL;DR

This study reveals that lattice symmetry changes are crucial for the metal-insulator transition in NdNiO3 films, with tensile strain inducing symmetry lowering and an MIT, unlike compressive strain.

Contribution

It demonstrates the importance of lattice symmetry in the MIT of NdNiO3 films using electron diffraction and symmetry analysis, clarifying microscopic mechanisms.

Findings

Symmetry lowering occurs in tensile strained films undergoing MIT.

No symmetry change is observed in compressively strained metallic films.

Results support bond length disproportionation as the MIT mechanism.

Abstract

Bulk NdNiO3 exhibits a metal-to-insulator transition (MIT) as the temperature is lowered that is also seen in tensile strained films. In contrast, films that are under a large compressive strain typically remain metallic at all temperatures. To clarify the microscopic origins of this behavior, we use position averaged convergent beam electron diffraction in scanning transmission electron microscopy to characterize strained NdNiO3 films both above and below the MIT temperature. We show that a symmetry lowering structural change takes place in case of the tensile strained film, which undergoes an MIT, but is absent in the compressively strained film. Using space group symmetry arguments, we show that these results support the bond length disproportionation model of the MIT in the rare-earth nickelates. Furthermore, the results provide insights into the non-Fermi liquid phase that is observed in films for which the MIT is absent.