Magnon supercurrent and the phase slippage in an yttrium iron garnet film

Exactly forty years ago, the spin superfluidity and Bose–Einstein condensation of magnons in superfluid antiferromagnetic $^3$He-B were discovered. In this work, the existence of spin superfluidity and phase slippage in an yttrium iron garnet film at room temperature is demonstrated using the optical Faraday effect. The $s$-patial distribution of the phase and amplitude of the spin precession under the conditions of magnon Bose–Einstein condensation are studied by varying the pump phase difference between two strip lines exciting magnons.