  Previously, it has been shown that rapid cooling of
yttrium-iron-garnet/platinum (Pt) nano structures, preheated by an electric
current sent through the Pt layer leads to overpopulation of a magnon gas and
to subsequent formation of a Bose-Einstein condensate (BEC) of magnons. The
spin Hall effect (SHE), which creates a spin-polarized current in the Pt layer,
can inject or annihilate magnons depending on the electric current and applied
field orientations. Here we demonstrate that the injection or annihilation of
magnons via the SHE can prevent or promote the formation of a rapid cooling
induced magnon BEC. Depending on the current polarity, a change in the BEC
threshold of -8% and +6% was detected. These findings demonstrate a new method
to control macroscopic quantum states, paving the way for their application in
spintronic devices.
