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

Abstract

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 SrIrO 3 /SrTiO 3 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.

Protonation-Induced Colossal Chemical Expansion and Property Tuning in NdNiO3 Revealed by Proton Concentration Gradient Thin Films

“…As shown in Figure c, after the protonation-induced phase transition, the (002) diffraction peak of NNO (2θ = 47.6°) disappeared and a new (002) diffraction peak associated with the formed H-NNO phase appeared at 41.8° (Figure c). The change in out-of-plane lattice constant indicates an colossal lattice expansion as large as 13% (from c pc,NNO = 3.81 Å to c pc,H‑NNO = 4.31 Å), which is much larger than previously reported protonation-induced lattice expansions: for example, H x SrCoO 2.5 , , H x WO 3 , , H x SrRuO 3 , H x SrIrO 3 , and H x CaRuO 3 (summarized in Table S1 in the Supporting Informatio). We note that this colossal chemical expansion is not likely caused by the formation of oxygen vacancies, since a vacuum annealing treatment can only lead to a maximum chemical expansion of ∼3.17% (Figure S4).…”

Protonation-Induced Colossal Lattice Expansion in La2/3Sr1/3MnO3

“…These changes, in turn, can induce quantum phase transitions and result in remarkable alterations in the electrical and magnetic properties. Compared to oxygen ion control, protonation offers significant prospects for ionic control with enhanced speed and faster response. , Thus, gaining insights into the diffusion behavior of protons within TMOs and their correlation with intrinsic factors such as strain is of utmost importance. It plays a critical role in designing and optimizing materials for proton-based magneto-ionics as well as for energy conversion purposes such as proton-conducting devices and fuel cells.…”

Realizing Metastable Cobaltite Perovskite via Proton-Induced Filling of Oxygen Vacancy Channels

“…Classical examples include the perovskite–brownmillerite topotactic phase transition of 3d TMOs (ABO x , B = Mn, Fe, and Co, x = 2.5–3) − and the formation of superconducting infinite-layer nickelates via topotactic reduction. − Recently, hydrogen (proton) control has also been gradually applied to a variety of oxide systems such as HSrCoO 2.5 , , H x ReNiO 3 (Re = rare-earth metals), − H x VO 2 , − H x -LSMO, and H x SrRuO 3 and exhibits its power in manipulating magnetoelectric behaviors of TMOs. Compared with O 2– , H + has much smaller size and better mobility, which creates more opportunities for ionic control with higher speed and faster response. , Therefore, understanding the interaction between TMOs and proton is a fundamental course for further investigating proton-based magneto-ionics as well as energy conversion applications such as protonic ceramic fuel cells (PCFCs).…”

“…Compared with O 2− , H + has much smaller size and better mobility, which creates more opportunities for ionic control with higher speed and faster response. 23,24 Therefore, understanding the interaction between TMOs and proton is a fundamental course for further investigating proton-based magneto-ionics as well as energy conversion applications such as protonic ceramic fuel cells (PCFCs).…”