  Spin-orbit-coupled Mott iridates show great similarity with parent compounds
of superconducting cuprates, attracting extensive research interests especially
for their electron-doped states. However, previous experiments are largely
limited within a small doping range due to the absence of effective dopants,
and therefore the electron-doped phase diagram remains elusive. Here we utilize
an ionic-liquid-gating induced protonation method to achieve electron-doping
into a 5d Mott-insulator built with SrIrO3/SrTiO3 superlattice, and achieve a
systematic mapping of its electron-doped phase diagram with the evolution of
the iridium valence state from 4+ to 3+, equivalent to doping of one electron
per iridium ion. Along increasing doping level, the parent Mott-insulator is
first turned into a localized metallic state with gradually suppressed magnetic
ordering, and then further evolved into a nonmagnetic band insulating state.
This work forms an important step forward for the study of electron-doped Mott
iridate systems, and the strategy of manipulating the band filling in an
artificially designed superlattice structure can be readily extended into other
systems with more exotic states to explore.
