  We theoretically manifest that the edge of a quantum spin Hall insulator
(QSHI), attached to an insulating ferromagnet (FM), can realize a highly
efficient spin-to-charge conversion. Based on a one-dimensional QSHI-FM
junction, the electron dynamics on the QSHI edge is analyzed, driven by a
magnetization dynamics in the FM. Under a large gap opening on the edge from
the magnetic exchange coupling, we find that the spin injection into the QSHI
edge gets suppressed while the charge current driven on the edge gets
maximized, demanded by the band topology of the one-dimensional helical edge
states.
