Local Temperature Control of Magnon Frequency and Direction of Supercurrents in a Magnon Bose-Einstein Condensate

Spatial variations in the saturation magnetization of magnetic samples, in which the magnon Bose-Einstein condensate is prepared, lead to the appearance of supercurrents and excitation of Bogoliubov waves, which can be exploited for data transfer and processing. Here, we show theoretically and experimentally that demagnetization fields arising in the magnetization landscape strongly influence the dynamics of magnon supercurrents. In our experiment, local laser heating of a tangentially magnetized film of yttrium iron garnet increases the magnetic field in the region of reduced magnetization and, as a result, elevates the bottom of the spin-wave spectrum, where Bose-Einstein condensate is formed. This causes a magnon supercurrent directed outward from the hot region.