We have performed an in situ angle-resolved photoemission spectroscopy study of undoped one-monolayer (1-ML) FeSe film on SrTiO3 to elucidate the nature of the parent phase of high-temperature superconductivity. Accurate tuning of carrier concentration at zero doping by low-temperature postgrowth annealing of the film enabled us to observe a linearly dispersive Dirac-cone band and a pointlike Fermi surface on the ΓM mirror reflection plane arising from the nematic order. Intriguingly, the low-energy excitations of this material are solely characterized by the Dirac-cone band, since no other bands cross the Fermi level unlike its multilayer counterpart. The present result strongly suggests that undoped 1-ML FeSe is a two-dimensional Dirac semimetal with a mirror-symmetry-protected Dirac-cone band.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics