title: Band structure evolution during the ultrafast ferromagnetic-paramagnetic phase transition in cobalt.
abstract: The evolution of the electronic band structure of the simple ferromagnets Fe, Co, and Ni during their well-known ferromagnetic-paramagnetic phase transition has been under debate for decades, with no clear and even contradicting experimental observations so far. Using time- and spin-resolved photoelectron spectroscopy, we can make a movie on how the electronic properties change in real time after excitation with an ultrashort laser pulse. This allows us to monitor large transient changes in the spin-resolved electronic band structure of cobalt for the first time. We show that the loss of magnetization is not only found around the Fermi level, where the states are affected by the laser excitation, but also reaches much deeper into the electronic bands. We find that the ferromagnetic-paramagnetic phase transition cannot be explained by a loss of the exchange splitting of the spin-polarized bands but instead shows rapid band mirroring after the excitation, which is a clear signature of extremely efficient ultrafast magnon generation. Our result helps to understand band structure formation in these seemingly simple ferromagnetic systems and gives first clear evidence of the transient processes relevant to femtosecond demagnetization.
authors.affiliation: University of Kaiserslautern and Research Center OPTIMAS, 67663 Kaiserslautern, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Eich
authors.affiliation: Forschungszentrum Jülich GmbH, Peter Grünberg Institut (PGI 6), 52425 Jülich, Germany.; Experimentalphysik Universität Duisburg-Essen, Lotharstraße 1, 47057 Duisburg,Germany.
authors.forename: Moritz
authors.initials: M
authors.lastname: Plötzing
authors.affiliation: University of Kaiserslautern and Research Center OPTIMAS, 67663 Kaiserslautern, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Rollinger
authors.affiliation: University of Kaiserslautern and Research Center OPTIMAS, 67663 Kaiserslautern, Germany.; Graduate School MAINZ, Gottlieb-Daimler-Strasse 47, 67663 Kaiserslautern, Germany.
authors.forename: Sebastian
authors.identifier: 0000-0002-7341-7136
authors.initials: S
authors.lastname: Emmerich
authors.affiliation: Forschungszentrum Jülich GmbH, Peter Grünberg Institut (PGI 6), 52425 Jülich, Germany.
authors.forename: Roman
authors.initials: R
authors.lastname: Adam
authors.affiliation: JILA, University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309-0440, USA.
authors.forename: Cong
authors.identifier: 0000-0002-7091-9878
authors.initials: C
authors.lastname: Chen
authors.affiliation: JILA, University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309-0440, USA.
authors.forename: Henry Cornelius
authors.identifier: 0000-0001-8386-6317
authors.initials: HC
authors.lastname: Kapteyn
authors.affiliation: JILA, University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309-0440, USA.
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Murnane
authors.affiliation: Forschungszentrum Jülich GmbH, Peter Grünberg Institut (PGI 6), 52425 Jülich, Germany.; Experimentalphysik Universität Duisburg-Essen, Lotharstraße 1, 47057 Duisburg,Germany.
authors.forename: Lukasz
authors.initials: L
authors.lastname: Plucinski
authors.affiliation: Georg-August-Universität Göttingen, I. Physikalisches Institut, 37077 Göttingen, Germany.
authors.forename: Daniel
authors.identifier: 0000-0001-7448-1167
authors.initials: D
authors.lastname: Steil
authors.affiliation: University of Kaiserslautern and Research Center OPTIMAS, 67663 Kaiserslautern, Germany.; Graduate School MAINZ, Gottlieb-Daimler-Strasse 47, 67663 Kaiserslautern, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Stadtmüller
authors.affiliation: Experimentelle Physik VI, Technische Universität Dortmund, 44221 Dortmund, Germany.
authors.forename: Mirko
authors.initials: M
authors.lastname: Cinchetti
authors.affiliation: University of Kaiserslautern and Research Center OPTIMAS, 67663 Kaiserslautern, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Aeschlimann
authors.affiliation: Forschungszentrum Jülich GmbH, Peter Grünberg Institut (PGI 6), 52425 Jülich, Germany.; Experimentalphysik Universität Duisburg-Essen, Lotharstraße 1, 47057 Duisburg,Germany.
authors.forename: Claus M
authors.identifier: 0000-0002-3920-6255
authors.initials: CM
authors.lastname: Schneider
authors.affiliation: Georg-August-Universität Göttingen, I. Physikalisches Institut, 37077 Göttingen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mathias
keywords: Stoner vs. Heisenberg picture; band-structure renormalization; correlated materials; femtomagnetism; high-harmonic generation; time-resolved photoemission