title: Single to Multiquasiparticle Excitations in the Itinerant Helical Magnet CeRhIn(5).
abstract: CeRhIn(5) is an itinerant magnet where the Ce(3+) spins order in a simple helical phase. We investigate the spin excitations and observe sharp spin waves parameterized by a nearest-neighbor exchange, J(RKKY)=0.88±0.05  meV. At higher energies, the spin fluctuations are heavily damped, where single-quasiparticle excitations are replaced by a momentum- and energy-broadened continuum constrained by kinematics of energy and momentum conservation. The delicate energy balance between localized and itinerant characters results in the breakdown of the single-quasiparticle picture in CeRhIn(5).
authors.affiliation: School of Physics and Astronomy and Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom.
authors.forename: C
authors.initials: C
authors.lastname: Stock
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.|Department of Materials Science, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Rodriguez-Rivera
authors.affiliation: Julich Centre for Neutron Science, Forschungszentrum Julich GmbH, Outstation at Institut Laue-Langevin, Boite Postale 156, 38042 Grenoble Cedex 9, France.
authors.forename: K
authors.initials: K
authors.lastname: Schmalzl
authors.affiliation: Department of Chemistry of Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: E E
authors.initials: EE
authors.lastname: Rodriguez
authors.affiliation: Institute Laue-Langevin, 71 Avenue des Martyrs, CS 20156, F-38042, Grenoble Cedex 9, France.
authors.forename: A
authors.initials: A
authors.lastname: Stunault
authors.affiliation: Department of Physics, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: C
authors.initials: C
authors.lastname: Petrovic