Substrate and cation engineering for optimizing superconductivity in infinite-layer nickelates

Abstract

In a recent experiment [Nature 642, 58 (2025)], a new record for the superconducting critical temperature $T_c$ among infinite-layer nickelates has been reported in doped SmNiO$_2$. Here, we use the cutting-edge dynamical vertex approximation (D$Γ$A), and qualitatively as well as quantitatively reproduce the $T_c$ vs. doping dome for this compound. Encouraged by this, we go further and identify a path towards realizing even higher $T_c$'s by changing the cation along the line Nd$\rightarrow$Sm$\rightarrow$Y$\rightarrow$Lu with matching substrates. The successively smaller cation radius allows for smaller lattice constants of the substrate. This in turn increases the in-plane hopping and thus eventually $T_c$.

Figures (3)

• Figure 1: $T_c$ vs. effective doping of SmNiO$_2$ (experiment: red triangles Chow2025; and theory: red squares) and LuNiO$_2$ (conjectured: open blue squares). The shaded area indicates a region where a competing antiferromagentic order could be expected, see text. Inset: Maximal $T_c$ vs. in-plane lattice constant for various substrates and matching cations $R$ as listed in Table \ref{['Table:hoppings']}; calculated values are shown with squares (red and blue refer to the compounds shown in the main figure), and the experimental data is taken from Li2020 for NdNiO$_2$ on STO and Lee2023 for NdNiO$_2$ on LSAT (green triangles), and Chow2025 for SmNiO$_2$ on NGO (red triangle). The theoretical $T_C$ marked by a black circle is from Kitatani2020.
• Figure 2: Filling of the $d_{x^2-y^2}$ orbital as a function of the total filling in the 10-orbital model, see the text, at inverse temperature $\beta=40$ eV$^{-1}$ ($T=290$ K) for the different IL nickelates studied.
• Figure 3: Fermi surfaces calculated with D$\Gamma$A at 58 K ($\beta=200$ eV$^{-1}$) for $n_{x^2-y^2}=0.75$, $0.85$ and $0.95$ in the $k_z=0$ plane. Top row: SmNiO$_2$@NGO, Middle row: YNiO$_2$@LAO, and Bottom row: LuNiO$_2$@YAP. Note that $n_{d_{x^2-y^2}}=0.75$ is not reached when doping SmNiO$_2$ since holes instead start to empty other 3$d$ orbitals in this doping range, see Fig. \ref{['Fig:mainFilling']}. The smaller $U/t$ ratio in LuNiO$_2$ does not lead to the emergence of a pseudogap any more, unlike in the Nd- (not shown), Sm- and Y-based compounds.