Local density of states and superconducting gap in the iron chalcogenide superconductor Fe1+δSe1-xTex observed by scanning tunneling spectroscopy

We report on the investigation of the quasiparticle local density of states and superconducting gap in the iron chalcogenide superconductor Fe1+delta Se1-xTex(T-c similar to 14 K). The surface of a cleaved crystal revealed an atomic square lattice, superimposed on the inhomogeneous background, with a lattice constant of similar to 3.8 A degrees without any reconstruction. Tunneling spectra measured at 4.2 K exhibit the superconducting gap, which completely disappears at 18 K, with a magnitude of similar to 2.3 meV, corresponding to 2 Delta/k(B)T(c)=3.8. In stark contrast to the cuprate superconductors, the value of the observed superconducting gap is relatively homogeneous, following a sharp distribution with a small standard deviation of 0.23 meV. Conversely, the normal-state local density of states observed above T-c shows spatial variation over a wide energy range of more than 1 eV, probably due to the excess iron present in the crystal.