title: Orbital-exchange and fractional quantum number excitations in an f-electron metal, Yb₂Pt₂Pb.
abstract: Exotic quantum states and fractionalized magnetic excitations, such as spinons in one-dimensional chains, are generally expected to occur in 3d transition metal systems with spin 1/2. Our neutron-scattering experiments on the 4f-electron metal Yb2Pt2Pb overturn this conventional wisdom. We observe broad magnetic continuum dispersing in only one direction, which indicates that the underlying elementary excitations are spinons carrying fractional spin-1/2. These spinons are the emergent quantum dynamics of the anisotropic, orbital-dominated Yb moments. Owing to their unusual origin, only longitudinal spin fluctuations are measurable, whereas the transverse excitations such as spin waves are virtually invisible to magnetic neutron scattering. The proliferation of these orbital spinons strips the electrons of their orbital identity, resulting in charge-orbital separation.
authors.affiliation: Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794, USA. Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY 11973, USA. Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: L S
authors.initials: LS
authors.lastname: Wu
authors.affiliation: Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794, USA. Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY 11973, USA. Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA.
authors.forename: W J
authors.initials: WJ
authors.lastname: Gannon
authors.affiliation: Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY 11973, USA. zaliznyak@bnl.gov.
authors.forename: I A
authors.initials: IA
authors.lastname: Zaliznyak
authors.affiliation: Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Tsvelik
authors.affiliation: Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Strasse 38, 01187 Dresden, Germany. Institute for Theoretical Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Brockmann
authors.affiliation: Institute for Theoretical Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands.
authors.forename: J-S
authors.initials: JS
authors.lastname: Caux
authors.affiliation: Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Kim
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Qiu
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
authors.forename: J R D
authors.initials: JR
authors.lastname: Copley
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: G
authors.initials: G
authors.lastname: Ehlers
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: A
authors.initials: A
authors.lastname: Podlesnyak
authors.affiliation: Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794, USA. Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, NY 11973, USA. Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Aronson