Fig. 1. Scanning Tunneling Microscopy on FeTe_0.55Se_0.45 with a superconducting tip.

a Atomically resolved topographic image (z-height map, 25 × 25 nm²) of FeTe_0.55Se_0.45 cleaved surface acquired with a Pb coated Pt/Ir tip (see inset) at 2.2 K in ultra-high vacuum. Setup condition: V_set = −8 mV, I_set = −100 pA. b, d, f Spatially averaged differential conductance spectra in the areas (r₁, r₂, r₃) marked by the black circles in a. r₁: no in-gap states. r₂: two in-gap resonances at ± 1.3 meV. r₃: two sets of peaks symmetric in energy around the Fermi level. c, e, g Deconvolution of the spectra shown in b, d, f, respectively, provide information about the intrinsic LDOS of the sample in the indicated areas. In r₂ a zero-bias impurity state is recovered and in r₃ two in-gap states are observed. Setup conditions: b V_set = 6 mV, I_set = 1.2 nA, d, f V_set = 5 mV, I_set = 2 nA. Lock-in modulation is $V_{\mathrm{mod}}=30$ μV peak-to-peak for all measured spectra.