Metal-insulator transition in composition-tuned nickel oxide films

Thin films of the solid solution Nd1−xLaxNiO3 are grown in order to study the expected 0 K phase transitions at a specific composition. We experimentally map out the structural, electronic and magnetic properties and an abrupt, possibly first order, insulator-metal transition is observed at x = 0.2. Raman spectroscopy and scanning transmission electron microscopy show that this is not associated with an abrupt global structural change. Density functional theory (DFT) and combined DFT and dynamical mean field theory (DFT-DMFT) calculations allow us to reproduce this behaviour just from thermodynamic considerations. Finally, resonant x-ray scattering and muon spin rotation suggest that coherent antiferromagnetism largely tracks the insulating phase around but that there are magnetic fluctuations in the system, possibly due to the first order nature of the 0 K transition.