Electronic coupling in nickelate-based superlattices

Rare earth nickelates are fascinating materials, well-known, for their metal to insulator transition (MIT) and unique antiferromagnetic ground state. Due to the lack of sizeable single crystals, heterostructures constitute the best system to study the fascinating properties of these materials [1]. Pursuant to this, we have grown superlattices made of SmNiO₃ and NdNiO₃ layers – two nickelates having different MIT temperatures. When these two compounds are brought together at an interface the stability of a metal-insulator phase separation can be controlled by the thickness of the individual layers with a critical length scale (Λ_c-MIT) below which, a single MIT occurs. Room temperature STEM-EELS confirmed that below Λ_c-MIT the entire structure is metallic whereas above Λ_c-MIT the NdNiO₃ layers are metallic and the SmNiO₃ layers insulating with a sharp electronic interface [2]. We propose that this behavior is controlled by the balance between the energy of the interfacial phase-boundary and the bulk phase energies [3].

To study how the magnetic order evolves in this complex multicomponent system, we combined resonant x-ray magnetic scattering and muon spin relaxation experiments. We found that, similar to what is observed in the resistivity measurements, these superlattices display either two magnetic transitions or one depending on the thickness of the individual layers. The critical length scale over which antiferromagnetic-paramagnetic phase coexistence can occur is found to be larger than the critical length scale for insulating-metallic phase coexistence. This behavior can be explained in terms of a phase boundary cost between magnetic and non-magnetic phases. 

Our simple model system allows us to better understand the coupling of the metal-to-insulator and magnetic transitions in systems sharing identical order parameters.

[1] S. Catalano, et al. Rep. Prog. Phys., (2017).

[2] B. Mundet, et al. Nano Lett., (2021).

[3] Domínguez, C. et al. Nat. Mat., (2020).