Bose-Einstein condensate of Dirac magnons*

A Dirac-like quasiparticle spectrum is generated for localized magnetic moments on a 2D honeycomb lattice. The bosonic nature of these excitations and pumping allow for an accumulation of Dirac bosons and open up the possibility of the Bose-Einstein condensation at the Dirac point.

We explore the formation and collective modes of the Bose-Einstein condensate of Dirac magnons (Dirac BEC). We derive a phenomenological multi-component model of pumped bosons together with bosons residing at Dirac nodes and study the dynamics of the condensates. The condensate coherence and its multi-component nature are manifested in the Rabi oscillations whose period is determined by a Haldane-like gap in the spin-wave spectrum. This gap also allows one to control the properties and stability of the collective modes.

A Dirac magnon BEC remains yet to be experimentally realized. We hope that our findings will stimulate the corresponding experimental search.