  The long charge carrier lifetime of the hybrid organic-inorganic perovskites
(HOIPs) is the key for their remarkable performance as a solar cell material.
The microscopic mechanism for the long lifetime is still in debate. Here, by
using muon spin relaxation technique that probes the fluctuation of local
magnetic fields, we show that the muon depolarization rate ($\Delta$) of a
prototype HOIP methylammonium lead iodide (MAPbI$_3$) shows a sharp decrease
with increasing temperature in two steps above 120 K and 190 K across the
structural transition from orthorhombic to tetragonal structure at 162 K. Our
analysis shows that the reduction of $\Delta$ is quantitatively in agreement
with the expected behavior due to the rapid development of MA jumping rotation
around the $C_3$ and $C_4$ symmetry axes. Our results provide direct evidence
for the intimate relation between the rotation of the electric dipoles of MA
molecules and the charge carrier lifetime in HOIPs.
