Low-Defect-Density Monolayer MoS Wafer by Oxygen-Assisted Growth-Repair Strategy.

Atomic chalcogen vacancy is the most commonly observed defect category in two dimensional (2D) transition-metal dichalcogenides, which can be detrimental to the intrinsic properties and device performance. Here a low-defect density, high-uniform, wafer-scale single crystal epitaxial technology by in situ oxygen-incorporated "growth-repair" strategy is reported. For the first time, the oxygen-repairing efficiency on MoS monolayers at atomic scale is quantitatively evaluated.

Initialization-Free and Magnetic Field-Free Spin-Orbit p-Bits with Backhopping-like Magnetization Switching for Probabilistic Applications.

Probabilistic bits (p-bits) with thermal- and spin torque-induced nondeterministic magnetization switching are promising candidates for performing probabilistic computing. Previously reported spin torque p-bits include volatile low-energy barrier nanomagnets (LBNMs) with spontaneously fluctuating magnetizations and initialization-necessary nonvolatile magnets. However, initialization-free nonvolatile spin torque p-bits are still lacking.

Analytical Photoresponses of Gated Nanowire Photoconductors.

Low-dimensional photoconductors have extraordinarily high photoresponse and gain, which can be modulated by gate voltages as shown in literature. However, the physics of gate modulation remains elusive. In this work, the physics of gate modulation in silicon nanowire photoconductors with the analytical photoresponse equations is investigated.

Anatomy of Hidden Dzyaloshinskii-Moriya Interactions and Topological Spin Textures in Centrosymmetric Crystals.

The Dzyaloshinskii-Moriya interaction (DMI) is understood to be forbidden by the symmetry of centrosymmetric systems, thus restricting the candidate types for investigating many correlated physical phenomena. Here, we report the hidden DMI existing in centrosymmetric magnets driven by the local inversion symmetry breaking of specific spin sublattices. The opposite DMI spatially localized on the inverse spin sublattice favors the separated spin spiral with opposite chirality.

Tunable Spin Textures in a Kagome Antiferromagnetic Semimetal via Symmetry Design.

Kagome antiferromagnetic semimetals such as MnSn have attracted extensive attention for their potential application in antiferromagnetic spintronics. Realizing high manipulation of kagome antiferromagnetic spin states at room temperature can reveal rich emergent phenomena resulting from the quantum interactions between topology, spin, and correlation. Here, we achieved tunable spin textures of MnSn through symmetry design by controlling alternate MnSn and heavy-metal Pt thicknesses.

Room-Temperature van der Waals Ferromagnet Switching by Spin-Orbit Torques.

The emerging wide varieties of the van der Waals (vdW) magnets with atomically thin and smooth interfaces hold great promise for next-generation spintronic devices. However, due to the lower Curie temperature of the vdW ferromagnets than room temperature, electrically manipulating its magnetization at room temperature has not been realized. In this work, it is demonstrated that the perpendicular magnetization of the vdW ferromagnet Fe GaTe can be effectively switched at room temperature in the Fe GaTe /Pt bilayer by spin-orbit torques (SOTs) with a relatively low current density of 1.

Electrically function-switchable magnetic domain-wall memory.

Versatile memory is strongly desired for end users, to protect their information in the information era. In particular, bit-level switchable memory that can be switched from rewritable to read-only function would allow end users to prevent important data being tampered with. However, no such switchable memory has been reported.

Large and tunable magnetoresistance in van der Waals ferromagnet/semiconductor junctions.

Magnetic tunnel junctions (MTJs) with conventional bulk ferromagnets separated by a nonmagnetic insulating layer are key building blocks in spintronics for magnetic sensors and memory. A radically different approach of using atomically-thin van der Waals (vdW) materials in MTJs is expected to boost their figure of merit, the tunneling magnetoresistance (TMR), while relaxing the lattice-matching requirements from the epitaxial growth and supporting high-quality integration of dissimilar materials with atomically-sharp interfaces. We report TMR up to 192% at 10 K in all-vdW FeGeTe/GaSe/FeGeTe MTJs.

High-Sensitivity and Fast-Speed UV Photodetectors Based on Asymmetric Nanoporous-GaN/Graphene Vertical Junction.

GaN-based photodetectors are strongly desirable in many advanced fields, such as space communication, environmental monitoring, . However, the slow photo-response speed in currently reported high-sensitivity GaN-based photodetectors still hinders their applications. Here, we demonstrate a high-sensitivity and fast-speed UV photodetector based on asymmetric Au/nanoporous-GaN/graphene vertical junctions.

Topological Spin Textures in a Non-Collinear Antiferromagnet System.

Topologically protected magnetic "whirls" such as skyrmions in antiferromagnetic materials have recently attracted extensive interest due to their nontrivial band topology and potential application in antiferromagnetic spintronics. However, room-temperature skyrmions in natural metallic antiferromagnetic materials with merit of probable convenient electrical manipulation have not been reported. Here, room-temperature skyrmions are realized in a non-collinear antiferromagnet, Mn Sn, capped with a Pt overlayer.

All-electrical switching of a topological non-collinear antiferromagnet at room temperature.

Non-collinear antiferromagnetic Weyl semimetals, combining the advantages of a zero stray field and ultrafast spin dynamics, as well as a large anomalous Hall effect and the chiral anomaly of Weyl fermions, have attracted extensive interest. However, the all-electrical control of such systems at room temperature, a crucial step toward practical application, has not been reported. Here, using a small writing current density of around 5 × 10 A·cm, we realize the all-electrical current-induced deterministic switching of the non-collinear antiferromagnet MnSn, with a strong readout signal at room temperature in the Si/SiO/MnSn/AlO structure, and without external magnetic field or injected spin current.

Selectively Controlled Ferromagnets by Electric Fields in van der Waals Ferromagnetic Heterojunctions.

Charge transfer plays a key role at the interfaces of heterostructures, which can affect electronic structures and ultimately the physical properties of the materials. However, charge transfer is difficult to manipulate externally once the interface is formed. The recently discovered van der Waals ferromagnets with atomically sharp interfaces provided a perfect platform for the electrical control of interfacial charge transfer.

Progress of GaN-Based Optoelectronic Devices Integrated with Optical Resonances.

Being direct wide bandgap, III-nitride (III-N) semiconductors have many applications in optoelectronics, including light-emitting diodes, lasers, detectors, photocatalysis, etc. Incorporation of III-N semiconductors with high-efficiency optical resonances including surface plasmons, distributed Bragg reflectors and micro cavities, has attracted considerable interests for upgrading their performance, which can not only reveal the new coupling mechanisms between optical resonances and quasiparticles, but also unveil the shield of novel optoelectronic devices with superior performances. In this review, the content covers the recent progress of GaN-based optoelectronic devices integrated with plasmonics and/or micro resonators, including the LEDs, photodetectors, solar cells, and light photocatalysis.

Current-assisted magnetization reversal in FeGeTe van der Waals homojunctions.

Among the numerous two-dimensional van der Waals (vdW) magnetic materials, FeGeTe (FGT), due to its outstanding properties such as metallicity, high Curie temperature and strong perpendicular magnetic anisotropy, has quickly emerged as a candidate with the most potential for the fabrication of all-vdW spintronic devices. Here, we fabricated a simple vertical homojunction based on two few-layer exfoliated FGT flakes. Under a certain range of external magnetic fields, the magnetization reversal can be achieved by applying a negative or positive pulse current, which can reduce the coercivity through the spin orbit torque of FGT itself in addition to the Joule heat.

A nanopillar-modified high-sensitivity asymmetric graphene-GaN photodetector.

Integration of two-dimensional (2D) materials with three-dimensional (3D) semiconductors leads to intriguing optical and electrical properties that surpass those of the original materials. Here, we report the high performance of a GaN nanopillar-modified graphene/GaN/Ti/Au photodetector (PD). After etching on the surface of a GaN film, GaN nanopillars exhibit multiple functions for improving the detection performance of the PD.

Large Tunneling Magnetoresistance in van der Waals Ferromagnet/Semiconductor Heterojunctions.

2D layered chalcogenide semiconductors have been proposed as a promising class of materials for low-dimensional electronic, optoelectronic, and spintronic devices. Here, all-2D van der Waals vertical spin-valve devices, that combine the 2D layered semiconductor InSe as a spacer with the 2D layered ferromagnetic metal Fe GeTe as spin injection and detection electrodes, are reported. Two distinct transport behaviors are observed: tunneling and metallic, which are assigned to the formation of a pinhole-free tunnel barrier at the Fe GeTe /InSe interface and pinholes in the InSe spacer layer, respectively.

Prospect of Spin-Orbitronic Devices and Their Applications.

Science, engineering, and medicine ultimately demand fast information processing with ultra-low power consumption. The recently developed spin-orbit torque (SOT)-induced magnetization switching paradigm has been fueling opportunities for spin-orbitronic devices, i.e.

Spin-Valve Effect in FeGeTe/MoS/FeGeTe van der Waals Heterostructures.

The van der Waals (vdW) materials offer an opportunity to build all-two-dimensional (all-2D) spintronic devices with high-quality interfaces regardless of the lattice mismatch. Here, we report on an all-2D vertical spin valve that combines a typical layered semiconductor MoS with vdW ferromagnetic metal FeGeTe (FGT) flakes. The linear current-voltage curves illustrate that Ohmic contacts are formed in FGT/MoS interfaces, while the temperature dependence of the junction resistance further demonstrates that the MoS interlayer acts as a conducting layer instead of a tunneling layer.

Magnetic Skyrmions in a Hall Balance with Interfacial Canted Magnetizations.

Magnetic skyrmions are attracting interest as efficient information-storage devices with low energy consumption, and have been experimentally and theoretically investigated in multilayers including ferromagnets, ferrimagnets, and antiferromagnets. The 3D spin texture of skyrmions demonstrated in ferromagnetic multilayers provides a powerful pathway for understanding the stabilization of ferromagnetic skyrmions. However, the manipulation mechanism of skyrmions in antiferromagnets is still lacking.

From two- to multi-state vertical spin valves without spacer layer based on FeGeTe van der Waals homo-junctions.

Different than covalently bonded magnetic multilayer systems, high-quality interfaces without dangling bonds in van der Waals (vdW) junctions of two-dimensional (2D) layered magnetic materials offer opportunities to realize novel functionalities. Here, we report the fabrication of multi-state vertical spin valves without spacer layers by using vdW homo-junctions in which exfoliated FeGeTe nanoflakes act as ferromagnetic electrodes and/or interlayers. We demonstrate the typical behavior of two-state and three-state magnetoresistance for devices with two and three FeGeTe nanoflakes, respectively.

Boost of single-photon emission by perfect coupling of InAs/GaAs quantum dot and micropillar cavity mode.

We proposed a precise calibration process of Al GaAs/GaAs DBR micropillar cavity to match the single InAs/GaAs quantum dot (QD) exciton emission and achieve cavity mode resonance and a great enhancement of QD photoluminescence (PL) intensity. Light-matter interaction of single QD in DBR micropillar cavity (Q ∼ 3800) under weak coupling regime was investigated by temperature-tuned PL spectra; a pronounced enhancement (14.6-fold) of QD exciton emission was observed on resonance.

Atomic origin of spin-valve magnetoresistance at the SrRuO grain boundary.

Defects exist ubiquitously in crystal materials, and usually exhibit a very different nature from the bulk matrix. Hence, their presence can have significant impacts on the properties of devices. Although it is well accepted that the properties of defects are determined by their unique atomic environments, the precise knowledge of such relationships is far from clear for most oxides because of the complexity of defects and difficulties in characterization.

Deterministic Magnetization Switching Using Lateral Spin-Orbit Torque.

Current-induced magnetization switching by spin-orbit torque (SOT) holds considerable promise for next generation ultralow-power memory and logic applications. In most cases, generation of spin-orbit torques has relied on an external injection of out-of-plane spin currents into the magnetic layer, while an external magnetic field along the electric current direction is generally required for realizing deterministic switching by SOT. Here, deterministic current-induced SOT full magnetization switching by lateral spin-orbit torque in zero external magnetic field is reported.

Hybrid light emitting diodes based on stable, high brightness all-inorganic CsPbI perovskite nanocrystals and InGaN.

Despite important advances in the synthesis of inorganic perovskite nanocrystals (NCs), the long-term instability and degradation of their quantum yield (QY) over time need to be addressed to enable the further development and exploitation of these nanomaterials. Here we report stable CsPbI perovskite NCs and their use in hybrid light emitting diodes (LEDs), which combine in one system the NCs and a blue GaN-based LED. Nanocrystals with improved morphological and optical properties are obtained by optimizing the post-synthesis replacement of oleic acid ligands with iminodibenzoic acid: the NCs have a long shelf-life (>2 months), stability under different environmental conditions, and a high QY, of up to 90%, in the visible spectral range.

Room-Temperature Nanoseconds Spin Relaxation in WTe and MoTe Thin Films.

The Weyl semimetal WTe and MoTe show great potential in generating large spin currents since they possess topologically protected spin-polarized states and can carry a very large current density. In addition, the intrinsic non-centrosymmetry of WTe and MoTe endows with a unique property of crystal symmetry-controlled spin-orbit torques. An important question to be answered for developing spintronic devices is how spins relax in WTe and MoTe.