Unexpected Zero Bias Conductance Peak on the Topological Semimetal Sb(111)

The expected signature of the long-sought Majorana fermion in a heterostructure of a superconductor and a topological material is a zero bias conductance peak (ZBCP). We use scanning tunneling microscopy (STM) to image the cleaved surface of the topological semimetal antimony (Sb), whose long surface-state lifetime and small critical thickness make it a good candidate for building such heterostructures. Its bilayer crystal structure is expected to cleave between bilayers, however we observed step heights corresponding to the intra-bilayer distance, indicating the presence of a broken bilayer on some terraces. The dI/dV spectra observed on these abnormal terraces are quite different from the usual Sb spectra and there is a pronounced ZBCP. Using quasiparticle interference imaging, Landau level spectroscopy and density functional theory, we found that the ZBCP originates from a van Hove singularity in the band structure due to the broken layer. We acknowledge funding from the National Science Foundation grant DMR-1410480 and the Canada Excellence Research Chair program.