Rare earth nickelates ReNiO3 have been intensively studied over the recent years for their magnetic properties as well as their very sharp metal-insulator transition. This transition can be tuned by the size of the rare-earth, so that the behavior changes in the series. LaNiO3, in particular, is metallic at all temperatures, making it an ideal electrode material for oxide-based electronics. This led to many subsequent investigations to unveil the tuning of their physical response to external parameters such as temperature and epitaxial strains.
Here, we report experimental investigations of ReNiO3 nickelates films (Re = La, Nd) on LAO substrates down to 3 unit cells by Raman spectroscopy, performed with the aim to explore the stability limit of the bulk structure for ultrathin films. This complements earlier results obtained on similar films down to 15 nm (approx. 40 unit cells), which had revealed a first symmetry lowering from the rhombohedral ground state of LaNiO3. Changes in the Raman signature for the ultrathin films give evidence for further structural changes. Methods for extraction of the Raman signature of those extremely thin films will also be discussed.
 M.C. Weber a,b, M. Guennou a, D. Pesquera c, J. Fontcuberta c, J. Íñiguez c, J. Kreisel a,b, Strain-induced symmetry breaking in LaNiO3 thin films, EMRS Fall meeting 2014.