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

Choubey, P. and Eremin, I.M.

Volume: 104 Pages:
DOI: 10.1103/PhysRevB.104.144504
Published: 2021

The recent scanning tunneling microscopy (STM) observation of -shaped and -shaped spectra (and their mixture) in superconducting thin films has been interpreted as the presence of two distinct gap symmetries in this nickelate superconductor [Gu, Nat. Commun.11, 6027 (2020)10.1038/s41467-020-19908-1]. Here, using a two-band model of nickelates capturing dominant contributions from Ni- and rare-earth (R)- orbitals, we show that the experimental observation can be simply explained within a pairing scenario characterized by a conventional -wave gap structure with the lowest harmonic on the Ni band and a -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 and mixed spectral line shapes depending on the position of the STM tip within the unit cell. The - and -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 -wave gap structure and the time-reversal symmetry-breaking gap which yields very similar intra-unit-cell spectra. © 2021 American Physical Society

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