Fractional spinon excitations in the triangular Heisenberg model

GONZALEZ M. G.; MANUEL, L. O.; GHIOLDI, E. A.; YOSHITOMO KAMIYA; TRUMPER, A. E.; SHANG-SHUN ZHANG; BATISTA, C. D.

Bariloche

Simposio; XXIII Latin American Symposium on Solid State Physics (SLAFES); 2018

We compute the zero temperature dynamical structure factor S(q,w) of the triangular lattice Heisenberg model using a Schwinger Boson approach that includes the Gaussian fluctuations (1/N correction) of the saddle point solution. While the ground state of this model exhibits a well-known 120 magnetic ordering, the excitation spectrum revealed by S(q,w) has a strong quantum character, which is not captured by low-order 1/S expansions. The low-energy magnons consist of two spinon bound states confined by the gauge fluctuations of the auxiliary field. This composite nature of the magnons leads to an internal structure of the magnon peaks. In addition, the continuum of high-energy spinon modes extends up to three times the single-magnon bandwidth. We find that several features of the magnetic excitation spectrum of the compound Ba_3CoSb_2O_9 can be interpreted by the present spinon-based theory.