title: End States and Subgap Structure in Proximity-Coupled Chains of Magnetic Adatoms.
abstract: A recent experiment [Nadj-Perge et al., Science 346, 602 (2014)] provides evidence for Majorana zero modes in iron (Fe) chains on the superconducting Pb(110) surface. Here, we study this system by scanning tunneling microscopy using superconducting tips. This high-resolution technique resolves a rich subgap structure, including zero-energy excitations in some chains. We compare the symmetry properties of the data under voltage reversal against theoretical expectations and provide evidence that the putative Majorana signature overlaps with a previously unresolved low-energy resonance. Interpreting the data within a Majorana framework suggests that the topological gap is smaller than previously extracted from experiment. Aided by model calculations, we also analyze higher-energy features of the subgap spectrum and their relation to high-bias peaks which we associate with the Fe d bands.
authors.affiliation: Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Ruby
authors.affiliation: Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany.
authors.forename: Falko
authors.initials: F
authors.lastname: Pientka
authors.affiliation: Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany.
authors.forename: Yang
authors.initials: Y
authors.lastname: Peng
authors.affiliation: Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: von Oppen
authors.affiliation: Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany.
authors.forename: Benjamin W
authors.initials: BW
authors.lastname: Heinrich
authors.affiliation: Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany.
authors.forename: Katharina J
authors.initials: KJ
authors.lastname: Franke