SmNiO₃/NdNiO₃ superlattices

Rare earth nickelates RNiO₃ (R≠La) stand out for their unique metal to insulator transition (MIT), accompanied by a symmetry lowering from an orthorhombic to a monoclinic structure. Moreover, they display an unusual antiferromagnetic ordering at T_Néel≤T_MI. Notably, the critical temperatures are a function of the Ni-O-Ni bond angle characterizing each member of the family and subtle changes in this angle can strongly modify the electronic behavior of the system. Bulk NdNiO₃ (NNO) shows T_Néel=T_MI, whereas for SmNiO₃ (SNO) T_MI>T_Néel. Strain allows these transitions to be tuned, but given the same substrate, it is always found that T_{MI_NNO}<T_{MI_SNO}. Here, we adopt a new strategy to inspect the evolution of structural distortions in RNiO₃-based heterostructures and their impact on the electronic properties by growing [n(SNO)/n(NNO)]_m superlattices (SLs). We have found that the T_MI and T_Néel of the whole system is controlled by the thickness of the individual SNO and NNO layers. For thicker SLs periods two separate MITs corresponding to those of the individual SNO and NNO layers are observed. However, the two separate MITs merge into a single one as the SL period is reduced. The relation between T_MI and T_Néel will also be investigated.