Anti-PbO-type CoSe film: A possible analog to FeSe superconductors

Quasi-two-dimensionality is well known as a key electronic and structural element of high temperature superconductivity. Here we prepared ultrathin films of anti-PbO-type CoSe down to the monolayer on a SrTiO₃(001) substrate using molecular beam epitaxy, and investigated their electronic structures by scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and transport measurements in combination with first-principles calculations. We found that the monolayer CoSe had similar band structure and non-ferromagnetism nature with monolayer FeSe on SrTiO₃, except for the Fermi level upshift by ∼0.25 eV and weaker electronic correlation with a renormalization factor of 1.7, due to extra electron filling from Co 3d⁷ compared with Fe 3d⁶. The results hint that superconductivity might emerge in hole-doped tetragonal CoSe films.