The spatial distributions of large gap-like structure on Fe(Se,Te) single crystals observed by STM/STS

•The nanoscale large gap VPG and small gap Δ maps of Fe(Se,Te) were observed by STS.•The STM topography shows clear atomic structure of ∼0.38 nm spacing.•The average of large gaps is |VPG| ∼ 305 mV with σ ∼ 48 mV.•The smallest gap magnitude Δ ∼ 7 meV was estimated by fitting curve.

The nanoscale spatial distributions of large gap-like structure on superconducting FeSe1−xTex were investigated by scanning tunneling microscopy/spectroscopy (STM/STS). The STM topography shows regular atomic lattice arrangements with the lattice spacing ∼0.38 nm, together with the randomly distributed large spots due to the excess Fe atoms. From the STS measurements, the small gap structures of Δ ∼ 7 meV were partly observed. On the other hand, the high-bias dI/dV curves exhibit the broad peak structures at the negative biases of VPG = −200 to −400 mV in the measured whole surface area. The average of these large gaps is |VPGave| ∼ 305 mV with the standard deviation of σ ∼ 48 mV. The spatial distributions of the VPG exhibit the domain structures consisting of the relatively smaller gaps (<250 meV), which correspond to the excess Fe positions. The small gap Δ ∼ 7 meV is also observed at those positions, suggesting that the excess Fe affects the electronic structures of FeSe1−xTex.