title: Collective nature of spin excitations in superconducting cuprates probed by resonant inelastic X-ray scattering.
abstract: We used resonant inelastic x-ray scattering (RIXS) with and without analysis of the scattered photon polarization, to study dispersive spin excitations in the high temperature superconductor YBa_{2}Cu_{3}O_{6+x} over a wide range of doping levels (0.1≤x≤1). The excitation profiles were carefully monitored as the incident photon energy was detuned from the resonant condition, and the spin excitation energy was found to be independent of detuning for all x. These findings demonstrate that the largest fraction of the spin-flip RIXS profiles in doped cuprates arises from magnetic collective modes, rather than from incoherent particle-hole excitations as recently suggested theoretically [Benjamin et al. Phys. Rev. Lett. 112, 247002 (2014)]. Implications for the theoretical description of the electron system in the cuprates are discussed.
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Minola
authors.affiliation: CNISM, CNR-SPIN and Dipartimento di Fisica, Politecnico di Milano, 20133 Milano, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Dellea
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Gretarsson
authors.affiliation: CNISM, CNR-SPIN and Dipartimento di Fisica, Politecnico di Milano, 20133 Milano, Italy.
authors.forename: Y Y
authors.initials: YY
authors.lastname: Peng
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Porras
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Loew
authors.affiliation: European Synchrotron Radiation Facility, 71 Avenue des Martyrs, Grenoble F-38043, France.
authors.forename: F
authors.initials: F
authors.lastname: Yakhou
authors.affiliation: European Synchrotron Radiation Facility, 71 Avenue des Martyrs, Grenoble F-38043, France.
authors.forename: N B
authors.initials: NB
authors.lastname: Brookes
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.|Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Y B
authors.initials: YB
authors.lastname: Huang
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Pelliciari
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Schmitt
authors.affiliation: CNISM, CNR-SPIN and Dipartimento di Fisica, Politecnico di Milano, 20133 Milano, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Ghiringhelli
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Keimer
authors.affiliation: CNISM, CNR-SPIN and Dipartimento di Fisica, Politecnico di Milano, 20133 Milano, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Braicovich
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Le Tacon