Strain mediated suppression of the metal-insulator transition in EuNiO3 thin films

TL;DR

This study demonstrates that strain in EuNiO3 thin films can suppress the metal-insulator transition, with compressive strain promoting metallic behavior through enhanced Ni-O covalence, as shown by structural and spectroscopic analyses.

Contribution

It reveals how strain engineering can control the electronic phase transition in EuNiO3 thin films, highlighting the role of covalence and lattice mismatch.

Findings

Compressive strain suppresses the metal-insulator transition.

Tensile strain maintains the insulating state with strong multiplet splitting.

Enhanced Ni-O covalence correlates with metallic behavior under strain.

Abstract

Ultrathin epitaxial films of EuNiO3 were grown on a series of substrates traversing highly compressive (- 2.4%) to highly tensile (2.5%) lattice mismatch. X-ray diffraction measurements showed the expected c-lattice parameter shift for compressive strain, but no detectable shift for tensilely strained substrates, while reciprocal space mapping confirmed the tensile strained film maintained epitaxial coherence. Transport measurements showed a successively (from tensile to compressive) lower resistance and a complete suppression of the metalinsulator transition at highly compressive lattice mismatch. Corroborating these findings, X-ray absorption spectroscopy measurements revealed a strong multiplet splitting in the tensile samples that progressively weakens with increasing compressive strain that, combined with cluster calculations, showed enhanced covalence between Ni-d and O-p orbitals leads to the metallic state.