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The solid solution Nd_1-xLa_xNiO₃ spans a range of materials properties. From NdNiO₃ (x = 0), a low temperature antiferromagnetic insulator with monoclinic symmetry to LaNiO₃ (x = 1) a metallic paramagnet with rhombohedral symmetry [1]. Using an intermittant sputtering technique, we grow high quality epitaxial thin films of this solid solution on various substrates and, in this way, achieve an analog control of the composition. We report here of an unexpected discontinuous electronic behaviour - an abrupt change from an insulating to a metallic groundstate - and establish a connection to the symmetries of the system. Our work sheds light on a little-explored area of the rare earth nickelate phase diagram.

[1]. Catalano S. et al, Rare-earth nickelates RNiO3: thin films and heterostructures, Rep. Prog. Phys. 81, (2018)