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Orbital-Exchange and Fractional Quantum Number Excitations in an f-electron Metal Yb2Pt2Pb



L. S. Wu, W. J. Gannon, I. A. Zaliznyak, A. M. Tsvelik, M. Brockmann, J.-S. Caux, M. S. Kim, Yiming Qiu, John R. Copley, G. Ehlers, A. Podlesnyak, M. C. Aronson


Exotic quantum states and fractionalized magnetic excitations, such as spinons in one-dimensional chains, are generally viewed as belonging to the domain of 3d transition metal systems with spin 1/2. Our neutron scattering experiments on the 4f-electron metal Yb2Pt2Pb overturn this common wisdom in an unexpected and spectacular way. 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 quantum dynamics of the anisotropic, orbital-dominated Yb moments, and thus these effective quantum spins are emergent variables that encode the electronic orbitals. The unique birthmark of their unusual origin is that only longitudinal spin fluctuations are measurable, while the transverse excitations such as spin waves are rendered wholly invisible to magnetic neutron scattering. The proliferation of these orbital-spinons strips the electrons of their orbital identity, and we thus report here a new electron fractionalization phenomenon, charge-orbital separation.


neutron scattering, orbital-spinon, charge-orbital separation


Wu, L. , Gannon, W. , Zaliznyak, I. , Tsvelik, A. , Brockmann, M. , Caux, J. , Kim, M. , Qiu, Y. , Copley, J. , Ehlers, G. , Podlesnyak, A. and Aronson, M. (2016), Orbital-Exchange and Fractional Quantum Number Excitations in an f-electron Metal Yb<sub>2</sub>Pt<sub>2</sub>Pb, Science, [online], (Accessed February 21, 2024)
Created June 2, 2016, Updated October 12, 2021