title: Low-energy (<10  meV) feature in the nodal electron self-energy and strong temperature dependence of the Fermi velocity in Bi{2}Sr{2}CaCu{2}O{8+δ}.
abstract: Using low photon energy angle-resolved photoemission, we study the low-energy dispersion along the nodal (π,π) direction in Bi{2}Sr{2}CaCu{2}O{8+δ} as a function of temperature. Less than 10 meV below the Fermi energy, the high-resolution data reveal a novel "kinklike" feature in the electron self-energy that is distinct from the larger well-known kink roughly 70 meV below E{F}. This new kink is strongest below the superconducting critical temperature and weakens substantially at higher temperatures. A corollary of this finding is that the Fermi velocity v{F}, as measured in this low-energy range, varies rapidly with temperature-increasing by almost 30% from 70 to 110 K. The behavior of v{F}(T) appears to shift as a function of doping, suggesting a departure from simple "universality" in the nodal Fermi velocity of cuprates.
authors.affiliation: Department of Physics, University of Colorado, Boulder, Colorado 80309-0390, USA. plumbnc@colorado.edu
authors.forename: N C
authors.initials: NC
authors.lastname: Plumb
authors.forename: T J
authors.initials: TJ
authors.lastname: Reber
authors.forename: J D
authors.initials: JD
authors.lastname: Koralek
authors.forename: Z
authors.initials: Z
authors.lastname: Sun
authors.forename: J F
authors.initials: JF
authors.lastname: Douglas
authors.forename: Y
authors.initials: Y
authors.lastname: Aiura
authors.forename: K
authors.initials: K
authors.lastname: Oka
authors.forename: H
authors.initials: H
authors.lastname: Eisaki
authors.forename: D S
authors.initials: DS
authors.lastname: Dessau