Probing atomic structure and Majorana wavefunctions in mono-atomic Fe chains on superconducting Pb surface

Motivated by the striking promise of quantum computation, Majorana bound states (MBSs) in solid-state systems have attracted wide attention in recent years. In particular, the wavefunction localisation of MBSs is a key feature and is crucial for their future implementation as qubits. Here we investigate the spatial and electronic characteristics of topological superconducting chains of iron atoms on the surface of Pb(110) by combining scanning tunnelling microscopy and atomic force microscopy. We demonstrate that the Fe chains are mono-atomic, structured in a linear manner and exhibit zero-bias conductance peaks at their ends, which we interpret as signature for a MBS. Spatially resolved conductance maps of the atomic chains reveal that the MBSs are well localised at the chain ends (≲25 nm), with two localisation lengths as predicted by theory. Our observation lends strong support to use MBSs in Fe chains as qubits for quantum-computing devices. Majorana bound states in one-dimensional nanowires have attracted wide attention in recent years due to their potential use as qubits for topological quantum computation based on braiding. Scientists at the University of Basel have assembled mono-atomic iron chains on the surface of superconducting lead Pb(110) and combined for the first time scanning tunneling microscopy and atomic force microscopy to spatially characterize the chains down to the atomic scale. The Majorana bound states appear as a zero-energy mode in the STM and as a pronounced halo in the AFM measurement at 5K, disappear above the superconducting state of lead and are well-localized at the chain ends (25 nm) with two localization lengths and wave function oscillations as predicted by theory. These observations thus lend strong support to the existence of Majorana bound states in hybrid Fe/Pb systems and provide strong motivation to use them as qubits for quantum computing devices.