Manipulation of the Electronic State of Mott Iridate Superlattice through Protonation Induced Electron‐Filling

Spin‐orbit‐coupled Mott iridates show great similarity with parent compounds of superconducting cuprates, attracting extensive research interest especially for their electron‐doped states. However, previous experiments have been largely limited within a small doping range due to the absence of effective dopants, and therefore the electron‐doped phase diagram remains elusive. Here, an ionic‐liquid‐gating‐induced protonation method is utilized to achieve electron‐doping into a 5d Mott‐insulator built with a SrIrO3/SrTiO3 superlattice (SL), and a systematic mapping of its electron‐doped phase diagram is achieved 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 evolves 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 SL structure can be readily extended into other systems with more exotic states to explore. Large modulation of the Hubbard band electron‐filling in 5d Mott iridate has been a long‐term challenge, which now is realized in a SrIrO3/SrTiO3 superlattice through electronically controlled protonation. With the electrons/protons doped, the Ir‐ions are tuned from +4 to +3, and an intriguing phase diagram from a Mott insulator to a localized metal and finally to a band insulator emerges