  Coherent wave states such as Bose-Einstein condensates (BECs), which
spontaneously form in an overpopulated magnon gas even at room temperature,
have considerable potential for wave-based computing and information processing
at microwave frequencies. The ability to control the transport properties of
magnon BECs plays an essential role for their practical use. Here, we
demonstrate spatio-temporal control of the BEC density distribution through the
excitation of magnon supercurrents in an inhomogeneously magnetized yttrium
iron garnet film. The BEC is created by microwave parametric pumping and probed
by Brillouin light scattering spectroscopy. The desired magnetization profile
is prepared by heating the film with optical patterns projected onto its
surface using a phase-based wavefront modulation technique. Specifically, we
observe a pronounced spatially localized magnon accumulation caused by magnon
supercurrents flowing toward each other originating in two heated regions. This
accumulation effect increases the BEC lifetime due to the constant influx of
condensed magnons into the confinement region. The shown approach to manipulate
coherent waves provides an opportunity to extend the lifetime of freely
evolving magnon BECs, create dynamic magnon textures, and study the interaction
of magnon condensates formed in different regions of the sample.
