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Ionic substitution forms an essential pathway to manipulate the structural phase, carrier density and crystalline symmetry of materials via ion-electron-lattice coupling, leading to a rich spectrum of electronic states in strongly correlated systems. Using the ferromagnetic metal SrRuO 3 as a model system, we demonstrate an efficient and reversible control of both structural and electronic phase transformations through the electric-field controlled proton evolution with ionic liquid gating. The insertion of protons results in a large structural expansion and increased carrier density, leading to an exotic ferromagnetic to paramagnetic phase transition. Importantly, we reveal a novel protonated compound of HSrRuO 3 with paramagnetic metallic as ground state. We observe a topological Hall effect at the boundary of the phase transition due to the proton concentration gradient across the film-depth. We envision that electric-field controlled protonation opens up a pathway to explore novel electronic states and material functionalities in protonated material systems. Ionic substitution is a useful way to manipulate structural, electronic, magnetic phase transitions in strongly correlated materials. Here, the authors report electric-field controlled protonation in SrRuO 3 , resulting in a large structural expansion and a ferromagnetic-to-paramagnetic phase transition.

The anomalous Hall effect (AHE) that emerges in antiferromagnetic metals shows intriguing physics and offers numerous potential applications. Magnets with a rutile crystal structure have recently received attention as a possible platform for a collinear-antiferromagnetism-induced AHE. RuO 2 is a prototypical candidate material, however the AHE is prohibited at zero field by symmetry because of the high-symmetry [001] direction of the Néel vector at the ground state. Here, we show AHE at zero field in Cr-doped rutile, Ru 0.8 Cr 0.2 O 2 . The magnetization, transport and density functional theory calculations indicate that appropriate doping of Cr at Ru sites reconstructs the collinear antiferromagnetism in RuO 2 , resulting in a rotation of the Néel vector from [001] to [110] while maintaining a collinear antiferromagnetic state. The AHE with vanishing net moment in the Ru 0.8 Cr 0.2 O 2 exhibits an orientation dependence consistent with the [110]-oriented Hall vector. These results demonstrate that material engineering by doping is a useful approach to manipulate AHE in antiferromagnetic metals. The anomalous Hall effect is typically associated with ferromagnets and referred to as anomalous due to its persistence even after the applied magnetic field is removed, due to the net magnetization of the ferromagnet. Recently there has been much interest in antiferromagnets that can host an anomalous Hall effect, despite a vanishing magnetization, and here, Wang et al observe an anomalous Hall effect in collinearly antiferromagnetic chromium doped RuO 2 .

Reducing the dimensionality of layered materials can result in properties distinct from their bulk crystals 1 – 3 . However, the emergent properties in atomically thin samples, in particular in metallic monolayer flakes, are often obtained at the expense of other important properties. For example, while Ising superconductivity—where the pairing of electrons with opposite out-of-plane spins from K and K′ valleys leads to an in-plane upper critical field exceeding the Pauli limit—does not occur in bulk NbSe 2 , it was observed in two-dimensional monolayer flakes 4 . However, the critical temperature was reduced as compared to bulk crystals 4 – 13 . Here we take a different route to control the superconducting properties of NbSe 2 by intercalating bulk crystals with cations from ionic liquids. This produces Ising superconductivity with a similar critical temperature to the non-intercalated bulk and is more stable than in a monolayer flake. Our angle-resolved photoemission spectroscopy measurements reveal the effectively two-dimensional electronic structure, and a comparison of the experimental electronic structures between intercalated bulk NbSe 2 and monolayer NbSe 2 film reveals that the intercalant induces electron doping. This suggests ionic liquid cation intercalation is an effective technique for controlling both the dimensionality and the carrier concentration, allowing tailored properties exceeding both bulk crystals and monolayer samples. The superconducting critical temperature of monolayer materials is often lower than their bulk counterparts. Now, intercalation is shown to induce two-dimensional superconducting properties while maintaining the bulk critical temperature.

Dielectric capacitors are vital for modern power and electronic systems, and accurate assessment of their dielectric properties is paramount. However, in many prevailing reports, the fringing effect near electrodes and parasitic capacitance in the test circuit were often neglected, leading to overrated dielectric performances. Here, the serious impacts of the fringing effect and parasitic capacitance are investigated both experimentally and theoretically on different dielectrics including Al 2 O 3 , SrTiO 3 , etc. The deviations are more critical for the measurements of capacitors using asymmetric electrodes with different areas and for dielectrics with a lower dielectric constant, and differences tested in silicone oil and air environments should be noticed. A method to calibrate the parasitic capacitance of the test circuit is also raised for ensuring the accuracy of measured dielectric performances. Enlarging the electrode diameter and/or thinning the sample can reduce the above deviations, and thus a general standard of setting capacitor configurations is proposed for the measurement validity. Our study clearly demonstrates that it is necessary to mitigate the fringing effect and subtract the parasitic capacitance to solve the problem on overrated dielectric performances, which is very important for the development of the dielectric research in a healthy and orderly way. The authors find that the dielectric performance of capacitors will be significantly overestimated due to the influences of fringing effect and parasitic capacitance. Methods to solve the problem are proposed to ensure measurement validity.

Multistate resistive switching device emerges as a promising electronic unit for energy-efficient neuromorphic computing. Electric-field induced topotactic phase transition with ionic evolution represents an important pathway for this purpose, which, however, faces significant challenges in device scaling. This work demonstrates a convenient scanning-probe-induced proton evolution within WO 3 , driving a reversible insulator-to-metal transition (IMT) at nanoscale. Specifically, the Pt-coated scanning probe serves as an efficient hydrogen catalysis probe, leading to a hydrogen spillover across the nano junction between the probe and sample surface. A positively biased voltage drives protons into the sample, while a negative voltage extracts protons out, giving rise to a reversible manipulation on hydrogenation-induced electron doping, accompanied by a dramatic resistive switching. The precise control of the scanning probe offers the opportunity to manipulate the local conductivity at nanoscale, which is further visualized through a printed portrait encoded by local conductivity. Notably, multistate resistive switching is successfully demonstrated via successive set and reset processes. Our work highlights the probe-induced hydrogen evolution as a new direction to engineer memristor at nanoscale. Designing efficient multistate resistive switching devices is promising for neuromorphic computing. Here, the authors demonstrate a reversible hydrogenation in WO 3 thin films at room temperature with an electrically-biased scanning probe. The associated insulator to metal transition offers the opportunity to precisely control multistate conductivity at nanoscale.

Chemical reduction in oxides plays a crucial role in engineering the material properties through structural transformation and electron filling. Controlling the reduction at nanoscale forms a promising pathway to harvest functionalities, which however is of great challenge for conventional methods (e.g., thermal treatment and chemical reaction). Here, we demonstrate a convenient pathway to achieve nanoscale chemical reduction for vanadium dioxide through the electron-beam illumination. The electron beam induces both surface oxygen desorption through radiolytic process and positively charged background through secondary electrons, which contribute cooperatively to facilitate the vacancy migration from the surface toward the sample bulk. Consequently, the VO 2 transforms into a reduced V 2 O 3 phase, which is associated with a distinct insulator to metal transition at room temperature. Furthermore, this process shows an interesting facet-dependence with the pronounced transformation observed for the c-facet VO 2 as compared with the a-facet, which is attributed to the intrinsically different oxygen vacancy formation energy between these facets. Remarkably, we readily achieve a lateral resolution of tens nanometer for the controlled structural transformation with a commercial scanning electron microscope. This work provides a feasible strategy to manipulate the nanoscale chemical reduction in complex oxides for exploiting functionalities. The authors demonstrate a nanoscale chemical reduction for VO 2 into V 2 O 3 through electron-beam illumination, showcasing potential for nanoscale manipulation of oxygen ionic evolution for advanced harvesting functionalities.

1T phase of transition metal dichalcogenides (TMDCs) formed by group 10 transition metals (e.g. Pt, Pd) have attracted increasing interests due to their novel properties and potential device applications. Synthesis of large scale thin films with controlled phase is critical especially considering that these materials have relatively strong interlayer interaction and are difficult to exfoliate. Here we report the growth of centimeter-scale PtTe, 1T-PtTe 2 and 1T-PtSe 2 films via direct deposition of Pt metals followed by tellurization or selenization. We find that by controlling the Te flux, a hitherto-unexplored PtTe phase can also be obtained, which can be further tuned into PtTe 2 by high temperature annealing under Te flux. These films with different thickness can be grown on a wide range of substrates, including NaCl which can be further dissolved to obtain free-standing PtTe 2 or PtSe 2 films. Moreover, a systematic thickness dependent resistivity and Hall conductivity measurements show that distinguished from the semiconducting PtSe 2 with hole carriers, PtTe 2 and PtTe films are metallic. Our work opens new opportunities for investigating the physical properties and potential applications of group 10 TMDC films and the new monochalcogenide PtTe film.

Recently discovered “sliding ferroelectrics” exhibit distinct polarization origin and switching mechanism compared to conventional ferroelectric materials. However, a clear understanding of the polarization switching kinetics remains lacking. Here, we demonstrate sub-nanosecond (0.6 ns) polarization switching in the sliding ferroelectrics WTe 2 , which is the fastest switching observed so far in van der Waals ferroelectrics. Furthermore, the conventional nucleation-limited-switching model can still be applied to describe the switching process. However, contrary to conventional ferroelectric materials, the activation field associated with polarization reversal increases with temperature. Theoretical analysis suggests that this behavior is linked to the charge transfer nature of polarization in WTe 2 and the unique sliding mechanism for polarization switching. Additionally, the device demonstrates remarkable endurance, with no fatigue observed after 10 10 switching cycles. This study provides valuable insights into the polarization reversal process in sliding ferroelectrics and paves the way for future advances in nanoelectronic and spintronic applications. The authors systematically investigate the polarization switching kinetics of sliding ferroelectric WTe 2 , demonstrating their ultrafast response (0.6 ns).

Hafnium oxide-based ferroelectric thin films are widely recognized as a CMOS-compatible and highly scalable material platform for next-generation non-volatile memory and logic devices. While out-of-plane ferroelectricity in hafnium oxide films has been intensively investigated and utilized in devices, purely in-plane ferroelectricity of hafnium oxides remains unexplored. In this work, we demonstrate a reversible structural modulation of the orthorhombic phase Hf 0.5 Zr 0.5 O 2 films between (111)-oriented [HZO(111) O ] multi-domain and (100)-oriented [HZO(100) O ] single-domain configurations by altering perovskite oxide buffer layers. Unlike conventional out-of-plane polarized HZO(111) O films, the HZO(100) O films exhibit uniaxial in-plane ferroelectric polarization, sustained even at a thickness of 1.0 nm. Furthermore, the in-plane ferroelectric switching achieves an ultralow coercivity of ~0.5 MV/cm. The HZO(100) O phase is stabilized by a staggered interfacial reconstruction, driven by the delicate interplays between symmetry mismatch and surface energy. These findings pave the way for innovative device designs and strategies for modulating the functionalities of hafnium oxide-based ferroelectrics. Moving beyond the widely studied (111)-oriented Hf 0.5 Zr 0.5 O 2 films, the authors demonstrate purely uniaxial in-plane ferroelectricity in orthorhombic (100)-oriented Hf 0.5 Zr 0.5 O 2 films, sustained even at a thickness of 1 nm.