Synthesis and X-Ray Absorption Spectroscopy of Nd_2−xSr_xNio₄ Thin Films (0 ≤ x ≤ 1.4)

Ruddlesden-Popper nickelates have been studied extensively over the last three decades due to their structural similarities to the high T_csuperconductivity cuprates. In particular, the layered nickelate La_2-xSr_xNiO₄is analogous to the high T_c superconductor, La_2-xSr_xCuO_4.Using reactive oxide molecular beam epitaxy (MBE), we synthesis Nd_2−xSr_xNiO₄, thin films for x = 0, 0.50, 1, 1.2, and 1.4. We observe metallic conductivity for x=1.2 and 1.4 thin films whereas the lower doping shows semiconducting transport over the full temperature range. We present polarization-dependent O-K and Ni-L_2,3 XAS spectra for our Sr-doped Nd₂NiO₄ thin films. We track the evolution of the oxygen-nickel hybridization, distribution of holes between O 2p and Ni 3d states and the nickel oxidation state across the series. Our results are consistent with previous work on bulk layered nickelates [1].<br/><br/>[1]. Uchida, M. et al. Pseudogap-related charge dynamics in the layered nickelate R_2−xSr_xNiO₄ (x∼1). Phys Rev B 86, 165126 (2012)<br/><br/>We acknowledge support from the US Department of Energy under award no. DE-SC0021925.