Towards unveiling elusive Majorana fermions in gold nanowires via STS

One-dimensional topological superconductor has inspired extensive theoretical work and spurred several experimental thrusts to explore Majorana fermions (MFs). A particularly promising theory involves combining the surface state of gold to an s-wave superconductor subjected to an applied field [1]. This system promises robust MFs protected by an intense Rashba spin-orbit coupling much larger than in semiconductor systems. Spatially well separated MFs are expected in long nanowires of Au, for an unambiguous detection of MFs. We studied scanning tunneling spectroscopy (STS) of Au nanowires long compared to the MF coupling length. STS shows clean superconducting gap induced in the surface state of Au via proximity effect. Using spatially resolved STS at ~ 400mK with a magnetic field applied along the wire, we demonstrate a pair of zero-bias bound states emerging at the ends of nanowire. While the observed non-local features nicely agree with the earlier theoretical prediction, our temperature and energy resolution is not sufficient to distinguish between MF and mini-gap state that are expected to exist at the end of a multi-channel wire. [1] Potter, A. C. and Lee, P. A., Phys Rev Lett 105, 227003 (2010).