Superconductivity in an infinite-layer nickelate superlattice.

Recent observations of superconductivity in infinite-layer nickelates offer insights into high-temperature superconductivity mechanisms. However, defects and dislocations in doped films complicate the realization of superconductivity, limiting current research to superconducting nickelate heterostructures. The lack of research on superconductivity in superlattices composed of ultrathin nickelates severely impedes not only the exploration of the interface effect on superconductivity, but also the utilization of heterostructure engineering for exploring higher superconducting temperature T.

Manipulation of Exchange Bias in Two-Dimensional van der Waals Ferromagnet Near Room Temperature.

As a host for exchange bias (EB), van der Waals (vdW) magnetic materials have exhibited intriguing and distinct functionalities from conventional magnetic materials. The EB in most vdW systems is far below room temperature, which poses a challenge for practical applications. Here, by using Kerr microscopy, we demonstrate a record-high blocking temperature that approaches room temperature and a huge positive EB field that nears 2 kOe at 100 K in naturally oxidized two-dimensional (2D) vdW ferromagnetic FeGaTe nanoflakes.

Hundred-Fold Enhancement in the Anomalous Hall Effect Induced by Hydrogenation.

The anomalous Hall effect (AHE) is one of the most fascinating transport properties in condensed matter physics. However, the AHE magnitude, which mainly depends on net spin polarization and band topology, is generally small in oxides and thus limits potential applications. Here, we demonstrate a giant enhancement of AHE in a LaCoO-induced 5d itinerant ferromagnet SrIrO by hydrogenation.

A broad-spectrum gas sensor based on correlated two-dimensional electron gas.

Designing a broad-spectrum gas sensor capable of identifying gas components in complex environments, such as mixed atmospheres or extreme temperatures, is a significant concern for various technologies, including energy, geological science, and planetary exploration. The main challenge lies in finding materials that exhibit high chemical stability and wide working temperature range. Materials that amplify signals through non-chemical methods could open up new sensing avenues.

Self-Optimized Ligand Effect of Single-Atom Modifier in Ternary Pt-Based Alloy for Efficient Hydrogen Oxidation.

Modifying the atomic and electronic structure of platinum-based alloy to enhance its activity and anti-CO poisoning ability is a vital issue in hydrogen oxidation reaction (HOR). However, the role of foreign modifier metal and the underlying ligand effect is not fully understood. Here, we propose that the ligand effect of single-atom Cu can dynamically modulate the d-band center of Pt-based alloy for boosting HOR performance.

Stoichiometry, Orbital Configuration, and Metal-to-Insulator Transition in NdSrNiO Films.

The discovery of superconductivity in the infinite-layer nickelate NdSrNiO has motivated tremendous efforts for its significance toward the understanding of high-temperature superconductivity. However, the synthesis of infinite-layer nickelates is instable and has become a hindrance to experimental progress. Optimizing the growth of precursor NdSrNiO by pulsed laser deposition is crucial for obtaining infinite-layer nickelates.

Controllable Itinerant Ferromagnetism in Weakly Correlated 5d SrIrO.

The weakly correlated nature of 5d oxide SrIrO determines its rare ferromagnetism, and the control of its magnetic order is even less studied. Tailoring structure distortion is currently a main route to tune the magnetic order of 5d iridates, but only for the spatially confined insulating counterparts. Here, we have realized ferromagnetic order in metallic SrIrO by construction of SrIrO/ferromagnetic-insulator (LaCoO) superlattices, which reveal a giant coercivity of ∼10 T and saturation field of ∼25 T with strong perpendicular magnetic anisotropy.

Development of highly efficient ultraviolet LEDs on hybrid patterned sapphire substrates.

A hybrid patterned sapphire substrate (HPSS) aiming to achieve high-quality Al(Ga)N epilayers for the development of GaN-based ultraviolet light-emitting diodes (UV LEDs) has been prepared. The high-resolution X-ray diffraction measurements reveal that the Al(Ga)N epilayers grown on a HPSS and conventional patterned sapphire substrate (CPSS) have similar structural quality. More importantly, benefiting from the larger refractive index contrast between the patterned silica array and sapphire, the photons can escape from the hybrid substrate with an improved transmittance in the UV band.

Strain-Induced Atomic-Scale Building Blocks for Ferromagnetism in Epitaxial LaCoO.

The origin of strain-induced ferromagnetism, which is robust regardless of the type and degree of strain in LaCoO (LCO) thin films, is enigmatic despite intensive research efforts over the past decade. Here, by combining scanning transmission electron microscopy with density functional theory calculations, we report that the ferromagnetism does not emerge directly from the strain itself but rather from the creation of compressed structural units within ferroelastically formed twin-wall domains. The compressed structural units are magnetically active with the rocksalt-type high-spin/low-spin order.

Emergent Ferroelectricity in Otherwise Nonferroelectric Oxides by Oxygen Vacancy Design at Heterointerfaces.

Introducing point defects in complex metal oxides is a very effective route to engineer crystal symmetry and therefore control physical properties. However, the inversion symmetry breaking, which is vital for many tantalizing properties, such as ferroelectricity and chiral spin structure, is usually hard to be induced in the bulk crystal by point defects. By designing the oxygen vacancy formation energy profile and migration path across the oxide heterostructure, our first-principles density functional theory (DFT) calculations demonstrate that the point defects can effectively break the inversion symmetry and hence create novel ferroelectricity in superlattices consisting of otherwise nonferroelectric materials SrTiO and SrRuO.

Growing a LaAlO/SrTiO heterostructure on CaNbO nanosheets.

The two-dimensional electron liquid which forms between the band insulators LaAlO (LAO) and SrTiO (STO) is a promising component for oxide electronics, but the requirement of using single crystal SrTiO substrates for the growth limits its applications in terms of device fabrication. It is therefore important to find ways to deposit these materials on other substrates, preferably Si, or Si-based, in order to facilitate integration with existing technology. Interesting candidates are micron-sized nanosheets of CaNbO which can be used as seed layers for perovskite materials on any substrate.

Spin chirality fluctuation in two-dimensional ferromagnets with perpendicular magnetic anisotropy.

Non-coplanar spin textures with scalar spin chirality can generate an effective magnetic field that deflects the motion of charge carriers, resulting in a topological Hall effect (THE). However, spin chirality fluctuations in two-dimensional ferromagnets with perpendicular magnetic anisotropy have not been considered so far. Here, we report evidence of spin chirality fluctuations by probing the THE above the Curie temperature in two different ferromagnetic ultra-thin films, SrRuO and V-doped SbTe.

Exploiting Symmetry Mismatch to Control Magnetism in a Ferroelastic Heterostructure.

In the bulk, LaCoO_{3} (LCO) is a paramagnet, yet the low-temperature ferromagnetism (FM) is observed in tensile strained thin films, and its origin remains unresolved. Here, we quantitatively measured the distribution of atomic density and magnetization in LCO films by polarized neutron reflectometry (PNR) and found that the LCO layers near the heterointerfaces exhibit a reduced magnetization but an enhanced atomic density, whereas the film's interior (i.e.

Nanoscale ferroelastic twins formed in strained LaCoO films.

The coexistence and coupling of ferroelasticity and magnetic ordering in a single material offers a great opportunity to realize novel devices with multiple tuning knobs. Complex oxides are a particularly promising class of materials to find multiferroic interactions due to their rich phase diagrams, and are sensitive to external perturbations. Still, there are very few examples of these systems.

Large orbital polarization in nickelate-cuprate heterostructures by dimensional control of oxygen coordination.

Artificial heterostructures composed of dissimilar transition metal oxides provide unprecedented opportunities to create remarkable physical phenomena. Here, we report a means to deliberately control the orbital polarization in LaNiO (LNO) through interfacing with SrCuO (SCO), which has an infinite-layer structure for CuO. Dimensional control of SCO results in a planar-type (P-SCO) to chain-type (C-SCO) structure transition depending on the SCO thickness.

Metal-insulator-transition engineering by modulation tilt-control in perovskite nickelates for room temperature optical switching.

In transition metal perovskites ABO, the physical properties are largely driven by the rotations of the BO octahedra, which can be tuned in thin films through strain and dimensionality control. However, both approaches have fundamental and practical limitations due to discrete and indirect variations in bond angles, bond lengths, and film symmetry by using commercially available substrates. Here, we introduce modulation tilt control as an approach to tune the ground state of perovskite oxide thin films by acting explicitly on the oxygen octahedra rotation modes-that is, directly on the bond angles.

Spin Direction-Controlled Electronic Band Structure in Two-Dimensional Ferromagnetic CrI.

Manipulating physical properties using the spin degree of freedom constitutes a major part of modern condensed matter physics and is a key aspect for spintronics devices. Using the newly discovered two-dimensional van der Waals ferromagnetic CrI as a prototype material, we theoretically demonstrated a giant magneto band-structure (GMB) effect whereby a change of magnetization direction significantly modifies the electronic band structure. Our density functional theory calculations and model analysis reveal that rotating the magnetic moment of CrI from out-of-plane to in-plane causes a direct-to-indirect bandgap transition, inducing a magnetic field controlled photoluminescence.

Oxygen Diode Formed in Nickelate Heterostructures by Chemical Potential Mismatch.

Deliberate control of oxygen vacancy formation and migration in perovskite oxide thin films is important for developing novel electronic and iontronic devices. Here, it is found that the concentration of oxygen vacancies (V ) formed in LaNiO (LNO) during pulsed laser deposition is strongly affected by the chemical potential mismatch between the LNO film and its proximal layers. Increasing the V concentration in LNO significantly modifies the degree of orbital polarization and drives the metal-insulator transition.

Quantum Anomalous Hall State in Ferromagnetic SrRuO_{3} (111) Bilayers.

SrRuO_{3} heterostructures grown in the (111) direction are a rare example of thin film ferromagnets. By means of density functional theory plus dynamical mean field theory we show that the half-metallic ferromagnetic state with an ordered magnetic moment of 2  μ_{B}/Ru survives the ultimate dimensional confinement down to a bilayer, even at elevated temperatures of 500 K. In the minority channel, the spin-orbit coupling opens a gap at the linear band crossing corresponding to 3/4 filling of the t_{2g} shell.

The swelling transition of lepidocrocite-type protonated layered titanates into anatase under hydrothermal treatment.

The common facets of anatase crystals are the (001) and (101) planes. However, the phase transformation from lepidocrocite-type titanate into anatase by hydrothermal processing yields an anatase microstructure with high concentration of exposed (010) planes. The phase transformation of a lepidocrocite-type protonated layered titanate (HTO) into anatase was studied using XRD, TEM, FTIR, and measurement of pH and zeta potential.

In situ TEM studies of oxygen vacancy migration for electrically induced resistance change effect in cerium oxides.

Oxide materials with resistance hysteresis are very promising for next generation memory devices. However, the microscopic dynamic process of the resistance change is still elusive. Here, we use in situ transmission electron microscopy method to study the role of oxygen vacancies for the resistance switching effect in cerium oxides.