title: Reconstruction of band structure induced by electronic nematicity in an FeSe superconductor.
abstract: We have performed high-resolution angle-resolved photoemission spectroscopy on an FeSe superconductor (T_{c}∼8  K), which exhibits a tetragonal-to-orthorhombic structural transition at T_{s}∼90  K. At low temperature, we found splitting of the energy bands as large as 50 meV at the M point in the Brillouin zone, likely caused by the formation of electronically driven nematic states. This band splitting persists up to T∼110  K, slightly above T_{s}, suggesting that the structural transition is triggered by the electronic nematicity. We have also revealed that at low temperature the band splitting gives rise to a van Hove singularity within 5 meV of the Fermi energy. The present result strongly suggests that this unusual electronic state is responsible for the unconventional superconductivity in FeSe.
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Nakayama
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Miyata
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan.
authors.forename: G N
authors.initials: GN
authors.lastname: Phan
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Sato
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Tanabe
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Urata
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan and WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Tanigaki
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan and WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Takahashi
mesh_terms: D004553:Electric Conductivity; D058085:Iron Compounds / Q000737:chemistry*; D056951:Photoelectron Spectroscopy / Q000379:methods; D012643:Selenium / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D058085:Iron Compounds; D012643:Selenium