Single-particle tunneling spectroscopy and superconducting gaps in the layered iron-based superconductor KCa2Fe4As4F2

We perform a scanning tunneling microscopy/spectroscopy study on the layered iron-based superconductor KCa2Fe4As4F2 with a critical temperature of about 33.5 K. Two types of terminated surfaces are generally observed after cleaving the samples in vacuum. On one commonly obtained surface, we observe a full gap feature with energy gap values close to 4.6 meV. This type of spectrum shows a clean and uniform full gap in space, which indicates the absence of gap nodes in this superconductor. Quasiparticle interference patterns have also been measured which show an intraband scattering pattern possibly due to the holelike alpha pocket. The Fermi energy of this band is only about 24 +/- 6 meV, as derived from the energy dispersion result. Meanwhile, impurity-induced bound-state peaks can be observed at about +/- 2.2 meV on some spectra, and the peak value seems to be independent of magnetic field. On the second type of surface, which is rarely obtained, the fully gapped feature can still be observed in the tunneling spectra, although multiple gaps are obtained from either a single spectrum or separate ones, and the gap values determined from coherence peaks locate mainly in the range from 4 to 7 meV. Our results clearly indicate the multiple and nodeless superconducting gap nature of the layered superconductor KCa2Fe4As4F2, and the superfluid is mainly contributed by the holelike Fermi surfaces near the Gamma point. This result should inspire further consideration of the effect of the shallow and incipient bands near the M point and help us to understand the pairing mechanism in this highly layered iron-based superconductor.

Automated summary

The study reveals that KCa2Fe4As4F2 is a layered iron-based superconductor with multiple and nodeless superconducting gap nature, with the superfluid mainly contributed by holelike Fermi surfaces.