Fundamental difference in the electronic reconstruction of infinite-layer vs. perovskite neodymium nickelate films on SrTiO₃(001)

Motivated by the recent observation of superconductivity in the infinite-layer nickelate NdNiO₂ on SrTiO₃(001) by Li et al. [1], we explore the effect of interface polarity on the electronic properties of NdNiO_n/SrTiO₃(001) (n = 2,3) by performing first-principles calculations including a Coulomb repulsion term [2]. For infinite-layer nickelate films (n = 2), electronic reconstruction drives the emergence of a 2DEG at the interface involving a strong occupation of the Ti 3d states. This effect is more pronounced than in LaAlO₃/SrTiO₃(001) and accompanied by a substantial reconstruction of the Fermi surface: a depletion of the self-doping Nd 5d states and an enhanced Ni e_g orbital polarization, reflecting a single hole in the 3d_x²_−y² states, i.e., cupratelike behavior. In contrast, no 2DEG forms for perovskite films (n = 3). We show that the topotactic reaction from the perovskite to the infinite-layer phase is confined to the nickelate film, whereas the SrTiO₃ substrate remains intact. Finally, we highlight differences between infinite-layer nickelate and cuprate films on SrTiO₃(001).

[1] D. Li et al., Nature 572, 624 (2019)
[2] B. Geisler and R. Pentcheva, Phys. Rev. B 102, 020502(R) (2020)