Electronic and magnetic properties of the NdNiO$_2$/SrTiO$_3$ thin films

TL;DR

The paper addresses how interface polarity and electron correlations at NdNiO2/SrTiO3 interfaces influence electronic and magnetic properties relevant to superconductivity in infinite-layer nickelates. It employs DFT+U with Ni 3d, Nd 4f, and Ti 3d states to study bulk NdNiO2 and capped/uncapped NdNiO2/SrTiO3(001) thin films under 0 and 20% Sr doping, analyzing changes in band structure and magnetism. The findings show pronounced, layer- and cap-dependent reconstructions of Ni–O–Nd states, with Nd 4f states generally pushed away from $E_F$ except in the 1L capped case, and with distinct magnetic orders emerging across different film geometries. These results underscore the critical role of interfacial physics and polar instabilities in shaping the electronic landscape that governs potential superconductivity in these oxide heterostructures, offering guidance for engineering interfaces to realize desired electronic phases.

Abstract

The hole-doped NdNiO$_2$ layer deposited on the SrTiO$_{3}$ surface exhibits unconventional superconductivity. Here, we present a systematic study of the electronic and magnetic properties of the NdNiO$_2$ superconductor using the density functional theory (DFT). The strong local Coulomb interactions in the Ni($3d)$ and Nd($4f$) states are included within the DFT+$U$ method. The effect of Sr doping on the electronic band structure and density of states was studied for the NdNiO$_2$ thin films deposited on the SrTiO$_3$ (001) surface. The results obtained for the uncapped thin films were compared with the calculations for the NdNiO$_2$ films capped by the SrTiO$_3$ layer. We have found significant changes in the electronic structure and magnetic properties of the thin films compared to the bulk crystal.

Figures (4)

• Figure 1: The tetragonal structures of (a) bulk $\mathrm{NdNiO_2}$ superconductor with the C-AFM order, (b) capped $\mathrm{NdNiO_2/SrTiO_3}$ (001) interface, and (c) uncapped $\mathrm{NdNiO_2/SrTiO_3}$ (001) interface are shown.
• Figure 2: The atom-projected (a,c) density of states (DOS) and (b,d) band structure of bulk $\mathrm{NdNiO_2}$ with the C-AFM order is shown for two cases: undoped (top), and 20% hole-doped (bottom).
• Figure 3: The orbital-resolved density of states of the (a-f) capped and (g-l) uncapped NdNiO$_2$/SrTiO$_3$(001) thin films is shown. The undoped and 20% hole-doped cases are marked with blue and red texts, respectively.
• Figure 4: The figure illustrates charge density ($\Delta \rho$) and magnetic moment differences upon doping for (a) bulk $\mathrm{NdNiO_2}$, (b) capped, and (c) uncapped NdNiO$_2$/SrTiO$_3$(001) thin films. Here, the yellow and cyan regions indicate electron accumulation and depletion, respectively. The distance between atoms along $c$ axis is shown after relaxation. The blue and red number shows magnetic moment (in $\mu_{B}$) for undoped and doped cases, respectively. In all plots, we set the isosurface level to $0.005~e/\text{\AA}^3$.