Localized electron polarons formed through the coupling of excess electrons and ionic vibrations play a key role in the functionalities of materials. However, the mechanism of the coexistence of ...delocalized electrons and localized polarons remains underexplored. Here, the discovery of high‐mobility 2D electron gas at the rutile TiO2 surfaces through argon ion irradiation induced oxygen vacancies is reported. Strikingly, the electron gas forms localized electronic states at lower temperatures, resulting in an abrupt metal–insulator transition. Moreover, it is found that the low‐temperature conductivity in the insulating state is dominated by excess free electrons with a high mobility of ≈103 cm2 V−1 s−1, whereas the carrier density is dramatically suppressed with decreasing temperature. Remarkably, it reveals that the application of an electric field can lead to a collapse of the localized states, resulting in a metallic state. These results reveal the strongly correlated/coupled nature between the localized electrons and high‐mobility electrons and offer a new pathway to probe and harvest the exotic electron states at the complex oxide surfaces.
High‐mobility electrons and localized electronic states can coexist at rutile TiO2 surfaces as induced through argon‐ion irradiation. Specifically, the localized states form robust shallow in‐gap states, leading to an exotic metal‐to‐insulator transition when cooling below a critical temperature. Furthermore, the localized states can be reactivated into free electrons through thermal heating or with external electric fields.
Freestanding oxide nanomembranes have promising applications because of their novel electronic states and flexible crystalline structures. Several materials have been developed as sacrificial layers ...to exfoliate thin films from substrates via wet‐etching. However, these materials face great challenges in terms of either complicated crystalline structures or corrosive solutions. Here, a new sacrificial material, SrCoO2.5, is presented, which can be coherently grown with wide‐range strains and crystalline orientations and is also soluble in eco‐friendly solutions such as acetic acid, vinegar, and even carbonated drinks. With SrCoO2.5 as the sacrificial layer, high‐quality freestanding ferromagnetic SrRuO3 membranes are achieved from wide‐range epitaxial strains and different crystalline orientations. By investigating the evolution of the magnetic properties of these samples, it is discovered that epitaxial strain causes a distinct modification of the magnetic anisotropy of (001)pc‐oriented SrRuO3 samples, while its influence on the (110)pc and (111)pc samples is insignificant. This study not only demonstrates the freestanding SrRuO3 as a promising material for flexible spintronic devices, but also offers a great opportunity to engineer a wide range of strained and oriented complex oxides for novel freestanding electronics using this newly developed sacrificial material.
Soluble materials used as sacrificial layers are highly desirable for engineering oxide nanomembranes. However, existing materials face challenges of complicated crystalline structures or corrosive solutions. This paper reports that SrCoO2.5, with a simple crystalline structure to adapt to various strains and orientations, is soluble in eco‐friendly solutions, offering an excellent opportunity to explore novel functionalities in freestanding complex oxides.
The commercial capacitor using dielectric biaxially oriented polypropylene (BOPP) can work effectively only at low temperatures (less than 105 °C). Polyphenylene oxide (PPO), with better heat ...resistance and a higher dielectric constant, is promising for capacitors operating at elevated temperatures, but its charge–discharge efficiency (η) degrades greatly under high fields at 125 °C. Here, SiO2 layers are magnetron sputtered on both sides of the PPO film, forming a composite material of SiO2/PPO/SiO2. Due to the wide bandgap and high Young’s modulus of SiO2, the breakdown strength (E b) of this composite material reaches 552 MV/m at 125 °C (PPO: 534 MV/m), and the discharged energy density (U e) under E b improves to 3.5 J/cm3 (PPO: 2.5 J/cm3), with a significantly enhanced η of 89% (PPO: 70%). Furthermore, SiO2/PPO/SiO2 can discharge a U e of 0.45 J/cm3 with an η of 97% at 125 °C under 200 MV/m (working condition in hybrid electric vehicles) for 20,000 cycles, and this value is higher than the energy density (∼0.39 J/cm3 under 200 MV/m) of BOPP at room temperature. Interestingly, the metalized SiO2/PPO/SiO2 film exhibits valuable self-healing behavior. These results make PPO-based dielectrics promising for high-temperature capacitor applications.
Localized electron polarons formed through the coupling of excess electrons and ionic vibrations play a key role in the functionalities of materials. However, the mechanism of the coexistence of ...delocalized electrons and localized polarons remains underexplored. Here, the discovery of high-mobility 2D electron gas at the rutile TiO
surfaces through argon ion irradiation induced oxygen vacancies is reported. Strikingly, the electron gas forms localized electronic states at lower temperatures, resulting in an abrupt metal-insulator transition. Moreover, it is found that the low-temperature conductivity in the insulating state is dominated by excess free electrons with a high mobility of ≈10
cm
V
s
, whereas the carrier density is dramatically suppressed with decreasing temperature. Remarkably, it reveals that the application of an electric field can lead to a collapse of the localized states, resulting in a metallic state. These results reveal the strongly correlated/coupled nature between the localized electrons and high-mobility electrons and offer a new pathway to probe and harvest the exotic electron states at the complex oxide surfaces.
The commercial capacitor using dielectric biaxially oriented polypropylene (BOPP) can work effectively only at low temperatures (less than 105 °C). Polyphenylene oxide (PPO), with better heat ...resistance and a higher dielectric constant, is promising for capacitors operating at elevated temperatures, but its charge-discharge efficiency (η) degrades greatly under high fields at 125 °C. Here, SiO
layers are magnetron sputtered on both sides of the PPO film, forming a composite material of SiO
/PPO/SiO
. Due to the wide bandgap and high Young's modulus of SiO
, the breakdown strength (
) of this composite material reaches 552 MV/m at 125 °C (PPO: 534 MV/m), and the discharged energy density (
) under
improves to 3.5 J/cm
(PPO: 2.5 J/cm
), with a significantly enhanced η of 89% (PPO: 70%). Furthermore, SiO
/PPO/SiO
can discharge a
of 0.45 J/cm
with an η of 97% at 125 °C under 200 MV/m (working condition in hybrid electric vehicles) for 20,000 cycles, and this value is higher than the energy density (∼0.39 J/cm
under 200 MV/m) of BOPP at room temperature. Interestingly, the metalized SiO
/PPO/SiO
film exhibits valuable self-healing behavior. These results make PPO-based dielectrics promising for high-temperature capacitor applications.
Berry curvature plays a crucial role in exotic electronic states of quantum materials, such as the intrinsic anomalous Hall effect. As Berry curvature is highly sensitive to subtle changes of ...electronic band structures, it can be finely tuned via external stimulus. Here, we demonstrate in SrRuO
thin films that both the magnitude and sign of anomalous Hall resistivity can be effectively controlled with epitaxial strain. Our first-principles calculations reveal that epitaxial strain induces an additional crystal field splitting and changes the order of Ru
orbital energies, which alters the Berry curvature and leads to the sign and magnitude change of anomalous Hall conductivity. Furthermore, we show that the rotation of the Ru magnetic moment in real space of a tensile-strained sample can result in an exotic nonmonotonic change of anomalous Hall resistivity with the sweeping of magnetic field, resembling the topological Hall effect observed in noncoplanar spin systems. These findings not only deepen our understanding of anomalous Hall effect in SrRuO
systems but also provide an effective tuning knob to manipulate Berry curvature and related physical properties in a wide range of quantum materials.
Ionic-liquid-gating- (ILG-) induced proton evolution has emerged as a novel strategy to realize electron doping and manipulate the electronic and magnetic ground states in complex oxides. While the ...study of a wide range of systems (e.g., SrCoO
, VO
, WO
, etc.) has demonstrated important opportunities to incorporate protons through ILG, protonation remains a big challenge for many others. Furthermore, the mechanism of proton intercalation from the ionic liquid/solid interface to whole film has not yet been revealed. Here, with a model system of inverse spinel NiCo
O
, an increase in system temperature during ILG forms a single but effective method to efficiently achieve protonation. Moreover, the ILG induces a novel phase transformation in NiCo
O
from ferrimagnetic metallic into antiferromagnetic insulating with protonation at elevated temperatures. This study shows that environmental temperature is an efficient tuning knob to manipulate ILG-induced ionic evolution.
Abstract The rapid development of artificial intelligence requires synaptic devices with controllable conductance updates and low power consumption. Currently, conductance updates based on identical ...voltage pulse scheme (IVPS) and nonidentical voltage pulse scheme (NIVPS) face drawbacks in terms of recognition accuracy and energy efficiency, respectively. In this study, a mixed voltage pulse scheme (MVPS) for tuning conductance is proposed to simultaneously achieve high recognition accuracy and high energy efficiency, and its superiority is experimentally verified based on high‐performance Au (or Ag)/PbZr 0.52 Ti 0.48 O 3 /Nb:SrTiO 3 ferroelectric tunnel junction (FTJ) synaptic devices. The MVPS‐based neural network simulation achieves a high recognition accuracy of ≈92% on the CIFAR10 dataset with better energy efficiency and throughput than those of NIVPS. In addition, high‐precision experimental vector‐matrix multiplication (with a relative error of ≈1.5%) is obtained, and the simulated FTJ synaptic arrays achieved a high inference energy efficiency of ≈85 TOPS W −1 and a throughput of ≈200 TOPS, which meets the requirements of artificial intelligence in low‐power scenarios. This study provides a possible solution for practical applications of FTJ in neural network computing.
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