Fig. 4. Development and stabilization of enhanced zero-energy LDOS at the ends with increasing chain length and the calculated topological phase diagram for the Fe chain.
(A) Measured zero-energy dI/dV profiles along the chains for (from bottom to the top) 3 to 12, 20, 30, and 40 Fe atoms. For clarity, the profiles are shifted vertically. (B) Comparison of the variation of zero-energy tunneling conductance between the middle and the ends of the chains with increasing number of atoms. The conductance values at the end are averaged over the positions indicated by the two dotted lines in the profiles, whereas the ones for the middle are averaged values from the regions around the center of the chains. The tunneling junctions were stabilized at IT = 5.0 nA and VS = 3.0 mV for all spectroscopic measurements. (C) Calculated topological phase diagram for a straight monoatomic Fe chain with noncollinear magnetization as a function of the on-site energy μ and spin splitting parameter J (section S3 and Supplementary Materials). Blue and gray shaded regions correspond to the topologically nontrivial superconducting phase and the trivial phase, respectively. The two dotted lines represent the parameters determined from ab initio calculations for Fe on the Re(0001) surface, μ = −0.92 eV and J = 2.18 eV.