Recent scanning tunneling microscopy (STM) observation of U-shaped and V-shaped spectra (and their mixture) in superconducting Nd1−xSrxNiO2 thin films has been interpreted as presence of two distinct gap symmetries in this nickelate superconductor [Gu et al., Nat. Comm. 11, 6027 (2020)]. Here, using a two-band model of nickelates capturing dominant contributions from Ni-3dx2−y2 and rare-earth (R)-5d3z2−r2 orbitals, we show that the experimental observation can be simply explained within a pairing scenario characterized by a conventional dx2−y2-wave gap structure with lowest harmonic on the Ni-band and a dx2−y2-wave gap with higher-harmonics on the R-band. We perform realistic simulations of STM spectra employing first-principles Wannier functions to properly account for the tunneling processes and obtain V, U, and mixed spectral line-shapes depending on the position of the STM tip within the unit cell. The V- and U-shaped spectra are contributed from Ni and R-bands, respectively, and Wannier functions, in essence, provide position-dependent weighing factors, determining the spectral line-shape at a given intra-unit cell position. We propose a phase-sensitive experiment to distinguish between the proposed d-wave gap structure and time-reversal symmetry breaking d+is gap which yields very similar intra-unit cell spectra.
@article{arxiv.2108.03916,
title = {Electronic Theory for Scanning Tunneling Microscopy Spectra in Infinite-Layer Nickelate Superconductors},
author = {Peayush Choubey and Ilya M. Eremin},
journal= {arXiv preprint arXiv:2108.03916},
year = {2021}
}