Correlated interface electron gas in infinite-layer nickelate versus cuprate films on SrTiO$_3$(001)

TL;DR

This study uses first-principles calculations to compare electronic reconstructions in nickelate and cuprate films on SrTiO3, revealing differences in interfacial electron gas density and doping effects that influence their electronic structures.

Contribution

It provides a comparative analysis of nickelate and cuprate interfaces, highlighting how polarity mismatch and rare-earth ions affect electron gas formation and doping.

Findings

Higher q2DEG carrier density in nickelates due to polarity mismatch.

Electrostatic doping is stronger in cuprates despite expectations.

NdNiO2 films on polar substrates suppress q2DEG and self-doping.

Abstract

Based on first-principles calculations including a Coulomb repulsion term, we identify trends in the electronic reconstruction of $A$NiO$_2$/SrTiO$_3$(001) ($A=$ Pr, La) and $A$CuO$_2$/SrTiO$_3$(001) ($A=$ Ca, Sr). Common to all cases is the emergence of a quasi-two-dimensional electron gas (q2DEG) in SrTiO$_3$(001), albeit the higher polarity mismatch at the interface of nickelates vs. cuprates to the nonpolar SrTiO$_3(001)$ substrate (${3+}/0$ vs. ${2+}/0$) results in an enhanced q2DEG carrier density. The simulations reveal a significant dependence of the interfacial Ti $3d_{xy}$ band bending on the rare-earth ion in the nickelate films, being $20$-$30\%$ larger for PrNiO$_2$ and NdNiO$_2$ than for LaNiO$_2$. Contrary to expectations from the formal polarity mismatch, the electrostatic doping in the films is twice as strong in cuprates as in nickelates. We demonstrate that the depletion of the self-doping rare-earth $5d$ states enhances the similarity of nickelate and cuprate Fermi surfaces in film geometry, reflecting a single hole in the Ni and Cu $3d_{x^2-y^2}$ orbitals. Finally, we show that NdNiO$_2$ films grown on a polar NdGaO$_3(001)$ substrate feature a simultaneous suppression of q2DEG formation as well as Nd~$5d$ self-doping.