title: High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides.
abstract: In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials.
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW, D-01069 Dresden, Germany.|Physics Department, University of California-San Diego, La Jolla, CA 92093, USA.
authors.forename: A
authors.initials: A
authors.lastname: Charnukha
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW, D-01069 Dresden, Germany.
authors.forename: D V
authors.initials: DV
authors.lastname: Evtushinsky
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.|Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich, Switzerland.
authors.forename: C E
authors.initials: CE
authors.lastname: Matt
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.|Institute of Condensed Matter Physics, 'Ecole Polytechnique F'ed'erale de Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: N
authors.initials: N
authors.lastname: Xu
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Shi
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW, D-01069 Dresden, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Büchner
authors.affiliation: Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich, Switzerland.
authors.forename: N D
authors.initials: ND
authors.lastname: Zhigadlo
authors.affiliation: Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich, Switzerland.
authors.forename: B
authors.initials: B
authors.lastname: Batlogg
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW, D-01069 Dresden, Germany.
authors.forename: S V
authors.initials: SV
authors.lastname: Borisenko