Unexpected Zero Bias Conductance Peak on the Topological Semimetal Sb(111) with a Broken Bilayer

Abstract

The long-sought Majorana fermion is expected to manifest in a topological-superconductor heterostructure as a zero bias conductance peak (ZBCP). As one promising platform for such heterostructures, we investigate the cleaved surface of the topological semimetal Sb(111) using scanning tunneling microscopy and spectroscopy. Remarkably, we find a robust ZBCP on some terraces of the cleaved surface, although no superconductor is present. Using quasiparticle interference imaging, Landau level spectroscopy and density functional theory, we show that the ZBCP originates from a van Hove singularity pushed up to the Fermi level by a sub-surface stacking fault. Amidst the sprint to stake claims on new Majorana fermion systems, our finding highlights the importance of using a local probe together with detailed modeling to check thoroughly for crystal imperfections that may give rise to a trivial ZBCP unrelated to Majorana physics.

Probing image potential states on the surface of the topological semimetal antimony

“…We observe bi-atomiclayer steps of the height 4.0 Å, as shown in Fig. 4(a), consistent with previous reports [17][18][19]. We acquire z(V ) spectra at each point on a line [inset of Fig.…”

Chiral $p-$wave superconductivity in Pb$_{1-x}$Sn$_{x}$Te: signatures from bound-state spectra and wavefunctions

“…35,54 The possibility of such errors arising in the interpretation of zero-bias anomalies have also been discussed in the context of other topological materials. 34 Using our exact analytical expressions, we show that the bound state wavefunctions for point defects in two dimensions decay monotonously as an inverse-square power law at large distances, without showing any Friedel-like oscillations. On the other hand, in the normal gap regime, the power-law states give way to conventional exponentially localized states upon the loss of superconducting order, which are qualitatively similar to subgap states in disordered semiconductors.…”

“…Indeed, such features may appear in point-contact spectroscopy measurements whenever the tunnel junction is not in the ballistic regime. 33 Similarly, zero-bias anomalies appearing in scanning tunneling spectra have been discussed extensively as signatures of Majorana bound states, [4][5][6]8 but may often originate from other independent causes such as bandstructure effects 34 and stacking faults. 35 Moreover, while it has been shown that Majorana bound states can indeed be realized at the end-points of linear defects in a chiral p−wave superconductor, 36 these may not exist for other types of surface defects, such as pointlike ones, or may be difficult to detect.…”