title: High-energy anomaly in the angle-resolved photoemission spectra of Nd(2-x)Ce(x)CuO₄: evidence for a matrix element effect.
abstract: We use polarization-dependent angle-resolved photoemission spectroscopy (ARPES) to study the high-energy anomaly (HEA) in the dispersion of Nd(2-x)Ce(x)CuO₄, x=0.123. We find that at particular photon energies the anomalous, waterfall-like dispersion gives way to a broad, continuous band. This suggests that the HEA is a matrix element effect: it arises due to a suppression of the intensity of the broadened quasiparticle band in a narrow momentum range. We confirm this interpretation experimentally, by showing that the HEA appears when the matrix element is suppressed deliberately by changing the light polarization. Calculations of the matrix element using atomic wave functions and simulation of the ARPES intensity with one-step model calculations provide further evidence for this scenario. The possibility to detect the full quasiparticle dispersion further allows us to extract the high-energy self-energy function near the center and at the edge of the Brillouin zone.
authors.affiliation: Helmholtz-Zentrum Berlin, Albert-Einstein-Strasse 15, D-12489 Berlin, Germany.
authors.forename: E D L
authors.initials: ED
authors.lastname: Rienks
authors.affiliation: Department of Physics, Tampere University of Technology, P.O. Box 692, FIN-33101 Tampere, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Ärrälä
authors.affiliation: Department of Physics, Tampere University of Technology, P.O. Box 692, FIN-33101 Tampere, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Lindroos
authors.affiliation: Center for Free-Electron Laser Science/DESY, Notkestrasse 85, D-22607 Hamburg, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Roth
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA and University of Science and Technology, Faculty of Physics and Applied Computer Science, 30-059 Krakow, Poland.
authors.forename: W
authors.initials: W
authors.lastname: Tabis
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: G
authors.initials: G
authors.lastname: Yu
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: M
authors.initials: M
authors.lastname: Greven
authors.affiliation: Helmholtz-Zentrum Berlin, Albert-Einstein-Strasse 15, D-12489 Berlin, Germany and Leibniz-Institute for Solid State and Materials Research Dresden, P.O. Box 270116, D-01171 Dresden, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Fink