Manipulating superconductivity of monolayer FeSe on graphene/SiC(0001) surface

Compared with those of bulk FeSe, the sizes of electron and hole pockets become smaller in monolayer FeSe because the absence of inter-layer coupling tends to narrow the energy band and decrease the overlap between electron and hole pockets in energy. For FeSe monolayer grown on graphene/SiC(0001) surface, we find the Fermi energy is in the range of a few meV. In addition, we demonstrate an approach to tuning the Fermi energy by the thickness of graphene layers. At the base temperature of STM, the film grown on trilayer graphene becomes superconducting with Δ=0.62meV. In contrast, no signature of superconductivity has been detected in the dI/dV spectra of FeSe monolayer on bilayer graphene. The FeSe monolayer on graphene/SiC(0001) has the potential to study the intriguing physics where the Fermi energy, the superconducting gap and the Zeeman energy in magnetic field are in the same order of magnitude.