Electrostatic control of the metal-insulator transition of ultrathin NdNiO$_{3}$ films

Rare earth nickelates (RNiO$_{3}$) exhibit a first order metal insulator transition upon cooling. Bulk studies on chemical doping indicated that both divalent and quatrovalent ions were effective in shifting T$_{MIT}$ to lower temperatures by $\sim$ 50 to 25 K for 1 \% hole and electron doping, respectively. However, separating the influence of structural distortions from band filling is particular important for the nickelates. Here we present a new approach to control the band-filling in nanoscale NdNiO$_{3}$ thin films by modulation doping. NdNiO$_{3}$ is remotely doped by interfacing it with a degenerately doped conventional band insulator, La-doped SrTiO$_{3}$. We show that the remote doping approach allows for purely electronic modulation of a carrier density in the absence of other structural changes. The proposed approach is experimentally tested using ultrathin (2.5 nm) NdNiO$_{3}$ films grown on La-doped SrTiO$_{3}$ films with different carrier concentrations. We show that remote doping systematically changes the charge carrier density in the NdNiO$_{3}$ film and causes a moderate shift ($\sim$ 20 K) in the metal-insulator transition temperature. These results will be discussed in the context of theoretical models of the materials exhibiting a metal-insulator transition.