title: Spin-orbital separation in the quasi-one-dimensional Mott insulator Sr2CuO3.
abstract: When viewed as an elementary particle, the electron has spin and charge. When binding to the atomic nucleus, it also acquires an angular momentum quantum number corresponding to the quantized atomic orbital it occupies. Even if electrons in solids form bands and delocalize from the nuclei, in Mott insulators they retain their three fundamental quantum numbers: spin, charge and orbital. The hallmark of one-dimensional physics is a breaking up of the elementary electron into its separate degrees of freedom. The separation of the electron into independent quasi-particles that carry either spin (spinons) or charge (holons) was first observed fifteen years ago. Here we report observation of the separation of the orbital degree of freedom (orbiton) using resonant inelastic X-ray scattering on the one-dimensional Mott insulator Sr2CuO3. We resolve an orbiton separating itself from spinons and propagating through the lattice as a distinct quasi-particle with a substantial dispersion in energy over momentum, of about 0.2 electronvolts, over nearly one Brillouin zone.
authors.affiliation: Paul Scherrer Institut, Swiss Light Source, CH-5232 Villigen PSI, Switzerland. justine.schlappa@helmholtz-berlin.de
authors.forename: J
authors.initials: J
authors.lastname: Schlappa
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authors.lastname: Wohlfeld
authors.forename: K J
authors.initials: KJ
authors.lastname: Zhou
authors.forename: M
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authors.lastname: Mourigal
authors.forename: M W
authors.initials: MW
authors.lastname: Haverkort
authors.forename: V N
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authors.lastname: Strocov
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authors.lastname: Hozoi
authors.forename: C
authors.initials: C
authors.lastname: Monney
authors.forename: S
authors.initials: S
authors.lastname: Nishimoto
authors.forename: S
authors.initials: S
authors.lastname: Singh
authors.forename: A
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authors.lastname: Revcolevschi
authors.forename: J-S
authors.initials: JS
authors.lastname: Caux
authors.forename: L
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authors.lastname: Patthey
authors.forename: H M
authors.initials: HM
authors.lastname: Rønnow
authors.forename: J
authors.initials: J
authors.lastname: van den  Brink
authors.forename: T
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authors.lastname: Schmitt