Josephson effects in a Bose–Einstein condensate of magnons

•We presented a theory that accounts for the collective dynamics of a magnon-BEC.•We discuss the nature of macroscopic interference between magnon-BEC clouds.•We remarked the close relation between the above phenomena and Josephson’s effect.•We remark the distinctive oscillations that characterize the Josephson oscillations.

A phenomenological theory is developed, that accounts for the collective dynamics of a Bose–Einstein condensate of magnons. In terms of such description we discuss the nature of spontaneous macroscopic interference between magnon clouds, highlighting the close relation between such effects and the well known Josephson effects. Using those ideas, we present a detailed calculation of the Josephson oscillations between two magnon clouds, spatially separated in a magnonic Josephson junction.