title: Direct observation of magnon fractionalization in the quantum spin ladder.
abstract: We measure by inelastic neutron scattering the spin excitation spectra as a function of applied magnetic field in the quantum spin-ladder material (C5H12N)2CuBr4. Discrete magnon modes at low fields in the quantum disordered phase and at high fields in the saturated phase contrast sharply with a spinon continuum at intermediate fields characteristic of the Luttinger-liquid phase. By tuning the magnetic field, we drive the fractionalization of magnons into spinons and, in this deconfined regime, observe both commensurate and incommensurate continua.
authors.affiliation: Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, CH-5232 Villigen, Switzerland.
authors.forename: B
authors.initials: B
authors.lastname: Thielemann
authors.forename: Ch
authors.initials: Ch
authors.lastname: Rüegg
authors.forename: H M
authors.initials: HM
authors.lastname: Rønnow
authors.forename: A M
authors.initials: AM
authors.lastname: Läuchli
authors.forename: J-S
authors.initials: JS
authors.lastname: Caux
authors.forename: B
authors.initials: B
authors.lastname: Normand
authors.forename: D
authors.initials: D
authors.lastname: Biner
authors.forename: K W
authors.initials: KW
authors.lastname: Krämer
authors.forename: H-U
authors.initials: HU
authors.lastname: Güdel
authors.forename: J
authors.initials: J
authors.lastname: Stahn
authors.forename: K
authors.initials: K
authors.lastname: Habicht
authors.forename: K
authors.initials: K
authors.lastname: Kiefer
authors.forename: M
authors.initials: M
authors.lastname: Boehm
authors.forename: D F
authors.initials: DF
authors.lastname: McMorrow
authors.forename: J
authors.initials: J
authors.lastname: Mesot