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Schwinger boson approach to magnetically ordered quantum magnets

ORAL

Abstract

The quest for quantum spin liquids is producing a large number of magnetically ordered quantum magnets that exhibit anomalies in their dynamical spin structure factor. These anomalies include a strong renormalization of the single-magnon bands and a broad continuum of excitations, whose integrated spectral weight is larger than the weight of the single-magnon peaks. These observations call for novel approaches that can properly capture the effect of strong quantum fluctuations. By considering a Schwinger boson theory (large-N approach) beyond the saddle-point approximation (N = ∞), we demonstrate that the inclusion of 1/N corrections is strictly necessary to remove unphysical modes (single-spinon poles) and to capture the true magnon modes, which emerge as two-spinon bound states (poles of the RPA propagator). Moreover, we show that for each Feynman diagram there is a counter-diagram that removes the unphysical single-spinon poles. The counter-diagrams are different for collinear and non-collinear orderings. Based on these results, we demonstrate that the large-N approach can exactly reproduce the spin-wave theory in the large-S limit.

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Presenters

  • Shang-Shun Zhang

    Department of Physics and Astronomy, University of Tennessee, Knoxville, Department of Physics and Astronomy, University of Tennessee, University of Tennessee, Knoxville

Authors

  • Shang-Shun Zhang

    Department of Physics and Astronomy, University of Tennessee, Knoxville, Department of Physics and Astronomy, University of Tennessee, University of Tennessee, Knoxville

  • Esteban Ghioldi

    Institute of Physics Rosario and National University of Rosario

  • Yoshitomo Kamiya

    Shanghai Jiao Tong University, Shanghai, China

  • Luis O. Manuel

    Institute of Physics Rosario and National University of Rosario

  • Adolfo Trumper

    Institute of Physics Rosario and National University of Rosario

  • Cristian Batista

    Physics and Astronomy, The University of Tennessee, Neutron Scattering Division and Shull-Wollan Center, Oak Ridge National Laboratory, Department of Physics and Astronomy, The University of Tennessee, University of Tennessee, Knoxville, Department of Physics and Astronomy, University of Tennessee, Knoxville, Department of Physics and Astronomy, University of Tennessee