Extended Data Fig. 2: Structural characterization of La2.79Sr0.21Ni2O7 films with varying La content.

a, XRD of 2.5-u.c.-thick La2.79Sr0.21Ni2O7 films on SrLaAlO4. b, The average and the standard deviation of the c-axis lattice constants. The optimal flux ratio for each Sr doping level x is calibrated using XRD measurements, by identifying the sample with a lattice constant of the smallest standard deviation (SD). The change of La content is controlled via La shutter time.