It is now well established that the Kitaev honeycomb model in a magnetic field along the [111]-direction harbors an intermediate gapless quantum spin liquid (QSL) phase sandwiched between a gapped non-abelian QSL at low fields H<Hc1 and a partially polarized phase at high fields H>Hc2. Here, we analyze the low field and high field phases and phase transitions in terms of single- and two-magnon excitations using exact diagonalization (ED) and density matrix renormalization group (DMRG) methods. We find that the energy to create a bound state of two-magnons Δp becomes lower than the energy to create a single spin flip Δs near Hc2. In the entire Kitaev spin liquid Δp<Δs and both gaps vanish at Hc2. We make testable predictions for magnon pairing that could be observable in Raman scattering measurements on Kitaev QSL candidate materials.
@article{arxiv.1908.10877,
title = {Two-Magnon Bound States in the Kitaev Model in a $[111]$-Field},
author = {Subhasree Pradhan and Niravkumar D. Patel and Nandini Trivedi},
journal= {arXiv preprint arXiv:1908.10877},
year = {2020}
}