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

Abstract

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 ∼0.38nm, together with the randomly distributed large spots due to the excess Fe atoms. From the STS measurements, the small gap structures of Δ∼7meV 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 −400mV in the measured whole surface area. The average of these large gaps is |VPGave|∼305mV with the standard deviation of σ∼48mV. The spatial distributions of the VPG exhibit the domain structures consisting of the relatively smaller gaps (<250meV), which correspond to the excess Fe positions. The small gap Δ∼7meV is also observed at those positions, suggesting that the excess Fe affects the electronic structures of FeSe1−xTex.