Renormalization of the nickelate phase diagram in strained thin films

As a result of strong electron-lattice coupling, the bulk electronic phase diagrams of correlated oxides can be modified in epitaxial thin films using reduced dimensionality and substrate-induced strain. Taking advantage of the unique features of these materials, such as correlation-driven magnetic and metal-insulator transitions, requires a systematic understanding of how the thin film phase diagram differs from the bulk. Here, we explore the phase diagram of thin films of rare-earth nickelates, $R$NiO$_3$, which in the bulk exhibit a systematic dependence of the transition temperature, $T_{MI}$, with $R$. Studying solid solutions of NdNiO$_3$ and LaNiO$_3$ (Nd$_y$La$_{1-y}$NiO$_3$ with $0 \leq y\leq 1$) under compressive epitaxial strain, we observe a consistent renormalization of $T_{MI}$ to lower temperatures. By examining the physical and electronic structure of the films using synchrotron x-ray diffraction and absorption spectroscopy, we determine that the renormalization is due to an enhanced Ni-O overlap as a result of coherent compressive strain.