ARPES Characterization of the Insulator-Metal Transition in Sr-Doped Nd₂NiO₄ Thin Films

The layered nickelates, <i>R</i>_2-xSr_xNiO₄ (<i>R</i> = trivalent rare-earth cation), and high-T_c cuprate superconductor, La_2-xSr_xCuO₄, are isostructural and both exhibit the suppression of antiferromagnetism, charge/spin strip order, and an insulator-metal transition upon hole-doping. However, no superconductivity has been observed in <i>R</i>_2-xSr_xNiO₄ to date. Differences in the electronic structure between the layered nickelates and cuprates may shed light on the key ingredients for high-temperature superconductivity. Here, we present the ARPES characterization of Nd_2-xSr_xNiO₄ (<i>x</i> = 0.8, 1.0, 1.2, and 1.4) thin films grown on LaAlO₃ (100). We observe a large hole pocket of x²-y² character at the M-point and an electron pocket of z² character at the Γ-point, consistent with previous work [1]. We track the volume of the electron and hole pockets upon hole-doping and characterize the quasi-particle peak across the insulator-metal transition at <i>x</i> = 1.0. Finally, we observe no <i>k_z</i>-dispersion in either the hole or electron pockets, in contrast to Eu_0.9Sr_1.1NiO₄ [1, 2] and the three-dimensional electronic structure of NdNiO₃.<br/><br/>[1] Uchida, M. et al. Phys Rev B <b>84</b>, 241109(R) (2011)<br/>[2] Uchida, M. <i>et al.</i> <i>Phys Rev B</i> <b>86</b>, 165126 (2012).<br/><br/>We acknowledge support from the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under award no. DE-SC0021925