Majorana-magnon crossover by a magnetic field in the Kitaev model*

Kitaev quantum spin liquids host Majorana fermions via the fractionalization of spins. In a magnetic field, the Majorana fermions were predicted to comprise a topological state with anionic excitations, which has attracted great attention by the recent discovery of the half-quantized thermal Hall conductivity. Nevertheless, a reliable theory remains elusive for the field effect, especially at finite temperature. Here we present unbiased large-scale numerical results for the Kitaev model in a wide range of magnetic field and temperature, obtained by continuous-time quantum Monte Carlo simulations. We find that the unconventional paramagnetic region showing fractional spin dynamics extends at finite temperature, far beyond the field range where the topological state is expected at zero temperature. Our results show the confinement-deconfinement behavior between the fractional Majorana excitations and the conventional magnons.
Ref. J. Yoshitake, J. Nasu, Y. Kato, and Y. Motome, preprint (arXiv:1907.07299)