Electronic theory for scanning tunneling microscopy spectra in infinite-layer nickelate superconductors

Abstract

The 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 the presence of two distinct gap symmetries in this nickelate superconductor [Gu et al., Nat. Commun. 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 the 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 by Ni and R bands, respectively, and Wannier functions, in essence, provide position-dependent weighting 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 the time-reversal symmetry-breaking d+is gap which yields very similar intra-unit-cell spectra.

Source-reported materials — not catalogue approval

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