Event Details

The **Yb^{3+}** ions in **Yb_2Pt_2Pb** 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 [1]. 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 [2]. 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. [1] M. S. Kim, et al., Phys. Rev. B. 77, 144425 (2008); K. Iwakawa et al., J. Phys. Soc. Jpn. 81, SB058 (2012); Y. Shimura et al., J. Phys. Soc. Jpn. 81 103601 (2012); M. S. Kim and M. C. Aronson, Phys. Rev. Lett. 110, 017201 (2013); W. Miiller et al., Phys. Rev. B 93, 104419 (2016). [2] L. S. Wu, W. J. Gannon et al., Science 352, 1206 (2016).