The Yb3+ ions in Yb2Pt2Pb form large, seemingly classical Ising magnetic moments, with
the large spin-orbit coupling of the 4f-electrons and the crystal electric field forming a J = +/-7/2 Yb
ground state doublet . However, from this unlikely host, emerges a continuum of quantum excitations
"spinons on one dimensional chains" in good agreement with the behavior expected for nearly
isotropic, S = +/-1/2, d-electron magnetic moments . These spinons, in a system who's magnetic
constituents are dominated by orbital moments, are robust and at low temperatures exist up to 2.3 T,
when all Yb magnetic moments become saturated. In magnetic fields larger than 0.5 T, the the spinon
gap is closed, modifying the quantum continuum through the formation of a fermi surface, leading to the
emergence of a longitudinally polarized interchain mode and spinon bound states along the chains. The
ground state doublet nature of the Yb ions ensures that at all fields, transverse excitations are virtually
nonexistent, giving unprecedented access to only the longitudinal excitation channel without the presence
of spin waves or other transverse damping mechanisms, allowing us to directly measure the dispersion
of this mode for the first time.
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