Origin of the V-shaped LDOS dip near the Fermi level in ultrathin FeSe on bilayer graphene/SiC(0001)

Determine the physical origin of the spatially anisotropic V-shaped suppression of the local density of states at the Fermi level observed by low-temperature scanning tunneling spectroscopy in monolayer, bilayer, and trilayer FeSe epitaxially grown on bilayer graphene/SiC(0001), which persists under out-of-plane magnetic fields up to 11 T and is therefore not attributable to superconductivity.

Background

The paper investigates epitaxial FeSe films grown on bilayer graphene/SiC(0001) and finds that monolayer to trilayer FeSe exhibit a dip-like feature in the tunneling density of states near the Fermi level at both 4.2 K and 340 mK. This feature is spatially anisotropic, varies in width and shape on the nanometer scale, and remains largely unchanged under out-of-plane magnetic fields up to 11 T, leading the authors to rule out a superconducting origin.

Similar dip-like features have been reported in other two-dimensional materials on graphene and have been attributed to mechanisms such as Coulomb blockade in the tunneling junction or phonon-assisted inelastic tunneling. However, for FeSe/BLG/SiC(0001) the underlying mechanism responsible for the observed non-superconducting dip at the Fermi level is not established in this work.