Probing the metal-insulator transition in nickelates using soft x-ray absorption spectroscopy

We have investigated the spectral changes occurring at the Ni-L-3,L-2 edge X-ray absorption spectrum of SmNiO3 epitaxial thin films as the temperature is varied across the metal-insulator transition. We show that in the low temperature insulating state, a clear multiplet structure gives rise to two peaks at the L-3 edge. As the temperature is increased the energy splitting between these peaks remains constant, being reduced only upon crossing the metal-insulator transition. We analyze films with varying strain-engineered metal-insulator transition temperatures and elucidate the separate effects of strain and temperature in the absorption spectra. (C) 2014 AIP Publishing LLC.