Strain Dependence of the Electronic Structure and Ferromagnetic Transition in the Cubic Perovskite BaRuO₃

It has been previously argued that the electronic density of states near the Fermi level plays a large role in the properties of perovskite ruthenates such as ferromagnetism and superconductivity. With a van Hove singularity observed in proximity to the Fermi level and a ferromagnetic transition at 60 K in bulk, the cubic perovskite (3C) polymorph of BaRuO₃ could provide an excellent platform to explore the relation between electronic structure and ferromagnetism in ruthenate systems. Here we employ epitaxial strain to study the evolution of the electronic and magnetic properties of 3C BaRuO₃ under varying degrees of biaxial strain. Using ozone-assisted molecular-beam epitaxy (MBE) in an adsorption-controlled growth regime, we obtain the first fully commensurately strained 3C BaRuO₃ thin films under strain states ranging from -1.2% to +0.4%. We observe the van Hove singularity near the Fermi level as well as a possible strain-driven Lifshitz transition via angle-resolved photoemission spectroscopy. Additionally, we find that the Curie temperature is enhanced to approximately 81 K under 0.4% tensile strain and decreases with lattice parameter until the ferromagnetism is completely suppressed under sufficient compressive strain.