  We study extremely nonequilibrium transport in correlated kagome magnet
Mn$_3$Sn by time-resolved terahertz Faraday rotation spectroscopy. When the
photoinjected carrier density exceeds $\sim$10$^{20}$ cm$^{-3}$, a cyclotron
resonance is clearly observed, signifying the emergence of unusual carriers
with 2000-times higher mobility than those in equilibrium. The result can be
attributed to a drastic change in the band structure owing to screening of the
electron correlation, highlighting the significant role of many-body effects in
this kagome compound in equilibrium. Our study opens up a new phase of
transport properties in correlated kagome materials under highly nonequilibrium
conditions.
