title: Two energy gaps and Fermi-surface "arcs" in NbSe2.
abstract: Using angle-resolved photoemission spectroscopy, we report on the direct observation of the energy gap in 2H-NbSe2 caused by the charge-density waves (CDW). The gap opens in the regions of the momentum space connected by the CDW vectors, which implies a nesting mechanism of CDW formation. In remarkable analogy with the pseudogap in cuprates, the detected energy gap also exists in the normal state (T>T0) where it breaks the Fermi surface into "arcs," it is nonmonotonic as a function of temperature with a local minimum at the CDW transition temperature (T0), and it forestalls the superconducting gap by excluding the nested portions of the Fermi surface from participating in superconductivity.
authors.affiliation: Leibniz-Institute for Solid State Research, IFW-Dresden, D-01171, Dresden, Germany.
authors.forename: S V
authors.initials: SV
authors.lastname: Borisenko
authors.forename: A A
authors.initials: AA
authors.lastname: Kordyuk
authors.forename: V B
authors.initials: VB
authors.lastname: Zabolotnyy
authors.forename: D S
authors.initials: DS
authors.lastname: Inosov
authors.forename: D
authors.initials: D
authors.lastname: Evtushinsky
authors.forename: B
authors.initials: B
authors.lastname: Büchner
authors.forename: A N
authors.initials: AN
authors.lastname: Yaresko
authors.forename: A
authors.initials: A
authors.lastname: Varykhalov
authors.forename: R
authors.initials: R
authors.lastname: Follath
authors.forename: W
authors.initials: W
authors.lastname: Eberhardt
authors.forename: L
authors.initials: L
authors.lastname: Patthey
authors.forename: H
authors.initials: H
authors.lastname: Berger