Surface <i>s</i>-wave superconductivity for oxide-terminated infinite-layer nickelates

We analyze the electronic structure of different surface terminations for infinite-layer nickelates. Surface NiO₂ layers are found to be buckled, in contrast to planar bulk layers. While the rare-earth terminated surface fermiology is similar to the bulk limit of the nickelates, the NiO₂ terminated surface band structure is significantly altered, originating from the effect of absence of rare-earth atoms on the crystal field splitting. Contrary to the bulk Fermi surfaces, there are two Ni-3d Fermi pockets, giving rise to enhanced spectral weight around the $\bar{M}$ point in the surface Brillouin zone. From a strong-coupling analysis, we obtain dominant extended s-wave superconductivity for the surface layer, as opposed to d-wave for the bulk. This finding distinguishes the nickelates from isostructural cuprates, where the analogous surface pairing mechanism is less pronounced. Our results are consistent with region-dependent gap structures revealed in recent STM measurements and provide an ansatz to interpret experimental data of surface-sensitive measurements on the infinite-layer nickelates.