Ultrafast magnetic and charge dynamics in confined NdNiO₃ superlattices

The rare-earth nickelates (RNiO₃) provide a model system for studying correlated electronic phenomena due to the existence of multiple forms of coupled electronic, magnetic, and structural order. NdNiO­₃ is a unique member of the family in which the paramagnetic-antiferromagnetic, metal-insulator, and charge ordering phase transitions all coincide in the bulk. When confined in NdNiO₃/NdAlO₃ superlattices, however, it was shown that these phase transitions split and the electronic ground state modified due to the influence of interfacial coupling and dimensionality. Here, we study the ultrafast electronic and magnetic dynamics in such superlattices upon photoexcitation using time-resolved resonant soft x-ray scattering and absorption spectroscopy. We observe the photo-induced melting of long-range antiferromagnetic order for different NdNiO₃ layer thicknesses, finding an enhanced magnetic stiffness in the thinnest layers relative to the bulk. We further compare the magnetic order parameter with measured changes in the Ni d orbital configuration on picosecond time scales to elucidate the impact of interfacial electronic reconstructions on the optically driven phase transition. This work demonstrates that atomically engineered heterostructures provide a general pathway to control non-equilibrium phases and dynamics in correlated systems.