Electrons Research Articles

Influence of orbital angular momentum of light on random spin-split modes in disordered anisotropic optical media

Spin–orbit interaction of light in a disordered anisotropic medium is known to yield spin split modes in the momentum domain because of the random spatial gradient of the geometric phase of light. Here, we have studied the statistics of such spin-split modes for beams carrying intrinsic orbital angular momentum through the quantification of momentum domain entropy and investigated its dependence on various beam parameters. The influence of the spatial structure of the beam and the phase vortex on the statistics of the spin split modes were separately investigated using input Laguerre–Gaussian and Perfect Vortex beams passing through a disordered anisotropic medium with controlled input disorder parameter, which was realized by modulating the pixels of a liquid crystal-based spatial light modulator. The results of systematic investigations on the impact of beam waist, spot size and topological charge of the vortex beam show that the influence of the spot size on the emergence of the random spin split modes is much more significant as compared to the other beam parameters.

Spin-orbit torque effect in silicon-based sputtered Mn3Sn film

Abstract Non-collinear antiferromagnet Mn3Sn has shown remarkable efficiency in charge-spin conversion, a novel magnetic spin Hall effect, and a stable topological antiferromagnetic state, which has resulted in great interest from researchers in the field of spin orbit torque. Current research has primarily focused on the spin orbit torque effect of epitaxially grown non-collinear antiferromagnet Mn3Sn films. However, this method is not suitable for large-scale industrial preparation. In this study, amorphous Mn3Sn films and Mn3Sn/Py heterostructures were prepared using a magnetron sputtering on silicon substrates. The spin torque-ferromagnetic resonance measurement demonstrated that only the conventional spin orbit torque effect generated by inplane polarized spin currents exists in the Mn3Sn/Py heterostructure, with a spin-orbit torque efficiency of 0.016. Additionally, we prepared the perpendicular magnetized Mn3Sn/CoTb heterostructure based on amorphous Mn3Sn film, where the spin-orbit torque driven perpendicular magnetization switching was achieved with a lower critical switching current density (3.9×107 A/cm2) compared to Ta/CoTb heterostructure. This research reveals the spin-orbit torque effect of amorphous Mn3Sn films and establishes a foundation for further advancement in the practical application of Mn3Sn materials in spintronic devices.

Bulk photovoltaic effect in Cu-doped LiNbO3 single crystals with controlled oxidation state

Abstract We investigate the bulk photovoltaic (PV) effect of Cu-doped LiNbO3 single crystals with various oxidation states of Cu. The Cu-doped samples exhibit the PV response under below-bandgap excitation, and the onset of photocurrent shifts depending on partial oxygen pressures (pO2) during the annealing treatment. Open-circuit voltages (V oc) under simulated sunlight (AM 1.5G) illumination are changed by pO2, and crystals annealed at pO2 = 1.0 × 10−10 atm exhibit the highest V oc of 1,700 V. Moreover, density functional theory (DFT) calculations for Cu-doped LiNbO3 cells with Cu2+ on the Li site and the Nb site indicate that half-filled gap states derived from 3d orbitals of Cu are formed within the bandgap. Based on Glass coefficients obtained by the analyses of polarization angle-dependent photocurrent densities and the DFT calculations, we consider that Cu2+ on the Li site is the major active site for the generation and separation of electron-hole pairs under visible light at hν = 2.4 eV.

Fabrication and characteristics study of self‐powered and UV–Vis–NIR photodetector based on p‐NiO:Eu nanofibers

AbstractHeterojunctions formed between undoped and Eu‐doped NiO nanofibers (NFs) and n‐Si were fabricated by electrospinning the NiO:Eu NFs onto Si. Since the photoresponse of the Eu‐doped NiO‐containing device was better than the undoped one, the study focused on the doped NiO‐containing device. This was explained by the increase in electron kinetics in terms of the active role of Eu in bonding with the 4f orbitals and the s, d, and f states of NiO. Electro‐optical measurements of the NiO:Eu NFs/n‐Si heterojunction were performed in the visible region depending on the light intensity and in the UV and NIR regions for 10 mW/cm2 powers. It was observed that the device exhibits a good level of rectification properties and responds very well to all lights. At all three light sources, the heterojunction photodetector exhibited self‐powered behavior. Furthermore, for 10 mW/cm2 light intensity, the NiO:Eu NFs/n‐Si photodetector achieved R values of 1.84 A/W at 365 nm, 0.98 A/W at 395 nm, and 1.54 A/W at 850 nm, while it is 0.12 A/W for visible light. Besides, the device showed an external quantum efficiency of 625% and this was attributed to the photocurrent gain. In self‐driven mode, D* values have been determined as 3.0 × 1012 Jones, 2.6 × 1012 Jones, and 2.9 × 1012 Jones for 365, 395, and 850 nm, respectively. The performance of NiO under UV light was attributed to the absorption of NiO under UV light, as well as the very good excitation of (Eu3+) ions by UV light.

Triboelectric Nanogenerators: State of the Art

The triboelectric nanogenerator (TENG), as a novel energy harvesting technology, has garnered widespread attention. As a relatively young field in nanogenerator research, investigations into various aspects of the TENG are still ongoing. This review summarizes the development and dissemination of the fundamental principles of triboelectricity generation. It outlines the evolution of triboelectricity principles, ranging from the fabrication of the first TENG to the selection of triboelectric materials and the confirmation of the electron cloud overlapping model. Furthermore, recent advancements in TENG application scenarios are discussed from four perspectives, along with the research progress in performance optimization through three primary approaches, highlighting their respective strengths and limitations. Finally, the paper addresses the major challenges hindering the practical application and widespread adoption of TENGs, while also providing insights into future developments. With continued research on the TENG, it is expected that these challenges can be overcome, paving the way for its extensive utilization in various real-world scenarios.

Spin orbit coupling enhanced thermionic cooling in two-dimensional semiconductor structures

We theoretically investigate the effect of Rashba spin–orbit coupling (RSO) on thermionics properties of two-dimensional semiconductor. Due to the hybridization of parabolic and linear energy dispersion, the thermal energy equipartition is modified. The thermionic emission from the lower spin branch is enhanced and that from the upper spin branch is reduced. For a double quantum well cooling structure under lower doping, the net heat transported through the structure is enhanced by RSO. The coefficient of performance (COP) is improved by about 20% in the low bias regime and around 3% in the high bias regime. Since the RSO can be further tuned by an applied field, the COP can be further optimized.

Enhancing microwave dielectric properties of Li4NbO4F for LTCC applications through tantalum ion doping

The atomic scale variation of tantalum ion doped Li4NbO4F ceramics is initially predicted through first principle calculations. Subsequently, Li4Nb(1-x)TaxO4F (0.00 ≤ x ≤ 0.10) ceramics are prepared using the solid phase reaction method. After sintering at 875 °C for 4hours, the Li4Nb0.96Ta0.04O4F ceramics exhibit optimum dielectric properties: εr = 14.73 ± 0.19, Q × f = 83,439 ± 2810GHz (@9.31GHz, improved by 41%), τf = - 28.33 ± 1.36 ppm/°C. Both the increase in relative density from 95.9 ± 0.32% to 96.2 ± 0.34% and the increase in grain size from 14.9 μm to 15.6 μm are non-intrinsic factors that contribute to the optimization of the dielectric properties. Instead, the internal factors suggest that the primary cause of the gradual decrease in εr is the redshift of the Raman wave number. The reduction in dielectric loss is attributable to the weakening of damping behavior, as well as the increase in lattice energy and electron cloud density. Finally, promising potential of Li4Nb0.96Ta0.04O4F ceramics for low-temperature co-fired ceramic (LTCC) applications is indicated by their favourable chemical compatibility with Ag electrodes.

Reconfigurable spintronic logic gate utilizing precessional magnetization switching

In traditional von Neumann computing architecture, the efficiency of the system is often hindered by the data transmission bottleneck between the processor and memory. A prevalent approach to mitigate this limitation is the use of non-volatile memory for in-memory computing, with spin–orbit torque (SOT) magnetic random-access memory (MRAM) being a leading area of research. In this study, we numerically demonstrate that a precise combination of damping-like and field-like spin–orbit torques can facilitate precessional magnetization switching. This mechanism enables the binary memristivity of magnetic tunnel junctions (MTJs) through the modulation of the amplitude and width of input current pulses. Building on this foundation, we have developed a scheme for a reconfigurable spintronic logic gate capable of directly implementing Boolean functions such as AND, OR, and XOR. This work is anticipated to leverage the sub-nanosecond dynamics of SOT-MRAM cells, potentially catalyzing further experimental developments in spintronic devices for in-memory computing.

Dual Exciton Polarization in Bipolar CeO2-x Nanocrystals Controlled by Defect-Based Redox Processes.

Discovering alternative means to control electronic states in semiconductor nanostructures is the key to the development of new quantum technologies. Controlling the cyclotron motion of free charge carriers in semiconductor nanocrystals using an external magnetic field generates a tunable angular momentum, as a collective electronic degree of freedom, which can be imparted to the electronic band states to achieve complete exciton polarization. The sign of this polarization is determined by the type of majority charge carriers in a given lattice. Using magnetic circular dichroism spectroscopy, we demonstrate a simultaneous polarization of excitonic states in substoichiometric oxygen-deficient CeO2-x nanocrystals associated with electrons and holes, which can be controlled by the thermal treatment of colloidal nanocrystals in oxidizing or reducing conditions. The presence of both occupied and unoccupied midgap states, due to Ce3+ 4f and Ce4+ 4f orbitals, respectively, allows for selective probing of the effect of holes in the valence band (VB → Ce4+ 4f) and electrons in the conduction band (Ce3+ 4f → CB). The two transitions show the opposite sign at 300 K due to the opposite angular momenta associated with cyclotron electrons and holes. The ability to manipulate Ce 4f-derived midgap states by defect formation during the synthesis or postsynthesis treatment allows for a range of new technological applications of CeO2-x nanocrystals in optoelectronics.

Inverse spin galvanic effect in proximitized superconductor/paramagnet systems

We show that the interplay between spin–orbit coupling (SOC) and the paramagnetic response of itinerant electrons in proximitized superconductor/paramagnet systems gives rise to the inverse spin galvanic effect, i.e., generation of magnetic moment under the influence of the charge current. Depending on the sign of the SOC constant and the system temperature, the corresponding contribution to the magnetic response of the superconductor can be either diamagnetic or paramagnetic. We discuss the relevance between the discovered phenomena and the recent experiments on Pt/Nb heterostructures as well as the puzzling sign change of the magnetic response observed in clean Ag coated Nb cylinders.

Antiferromagnetism in two-dimensional materials: progress and computational challenges

We present a perspective on the status of antiferromagnetism in two-dimensional (2D) materials. Various types of spin-compensated orders are discussed and include non-collinear order, spin spirals and altermagnetism. Spin–orbit effects ultimately determine, whether compounds exhibit long range order, Kosterlitz-Thouless physics, or multiferroic properties and we discuss the basic magnetic prototypes that may arise in 2D materials depending on the magnetic anisotropy and ordering vector. A summary of 2D antiferromagnets that have been characterized experimentally is provided—with particular emphasis on magnetic anisotropies and Neel temperatures. We then outline the ingredients needed to describe the magnetic properties using density functional theory. In particular, the systematic determination of magnetic ground states from the generalized Bloch theorem and the magnetic force theorem, which may be used to calculate magnetic excitations from the Heisenberg model with parameters determined from first principles. The methods are exemplified by application to the monolayer helimagnet NiBr2. Finally, we present a summary of predicted and prospective 2D antiferromagnets and discuss the challenges associated with the prediction of Néel temperatures from first principles.

Low-Migration Compounds with Amine Functionality as Coinitiators of Radical Polymerization.

The utilization of two-component systems comprising camphorquinone (CQ) and aromatic amines has become prevalent in the photopolymerization. However, there are still concerns about the safety of this CQ/amine system, mainly because of the toxicity associated with the leaching of aromatic amines. In light of these concerns, this study aims to develop novel coinitiator combinations featuring CQ and amines which cannot be leached out of materials, enabling free radical polymerization of representative dentalmethacrylate resins under blue light irradiation. This approach involves the initial design and analysis of hydrogen donors with low C─H bond dissociation energy through molecular modeling. Subsequently, copolymerizable methacrylate functional groups are incorporated via chemical modification, allowing it to act as both coinitiator and copolymerization monomer to achieve low migrationand leachability properties. This work presents, for the first time, the synthesis of the innovative coinitiator and compares its performance with the benchmark CQ/ethyl-4-dimethylaminobenzoate (EDB)-based photoinitiation system (PIS). The results demonstrate the effectiveness of the newly proposed PIS. Finally, an in-depth investigation is conducted into the reaction mechanism associated with this PIS through molecular orbital calculations and electron spin resonance studies.

Navigating the 18-n+m Isomers of PdSn2: Chemical Pressure Relief through Isolobal Bonds and Main Group Clustering.

The 18-n electron-counting rule provides structural guidelines for electronically feasible transition metal (T)-main group (E) phases, contributing toward the goal of material design. However, the availability of numerous potential structure types at any electron count creates a challenge for the prediction of the preferred structures of specific compounds, as is illustrated by the concept of 18-n+m isomerism. In this Article, we explore the driving forces stabilizing one 18-n+m isomer over another with an analysis of the structure of PdSn2, a layered intergrowth of the fluorite and CuAl2 structure types. The DFT-reversed approximation Molecular Orbital (DFT-raMO) method reveals that PdSn2 and its hypothetical parent structures all adhere to bonding schemes approximating the electronic configurations expected from the 18-n rule, with various degrees of isolobal Pd-Pd bonding and Sn clustering. However, partial electron transfer between the Pd 5p orbitals to the Sn 5s orbitals contributes to the absence of convincing electronic pseudogaps near their Fermi energies. As such, there is no clear electronically driven preference among the structure types. This situation allows for atomic packing effects to prevail: DFT-Chemical Pressure (DFT-CP) analysis illustrates that in the fluorite-type parent structure, positive Pd-Sn CPs lead to overcompression of the Pd atoms and a stretching of the relatively open Sn sublattice. In contrast, in the CuAl2-type parent structure, Sn atoms cluster into tetrahedra, opening space for an expanded Pd environment and the formation of Pd-Pd interactions. However, the tetrahedral packing of the Sn atoms here leads to frustration between negative and positive Sn-Sn CPs. Through the development of the angular CP correlation function (CPcor+) as a tool to quantify frustration among interatomic interactions, we demonstrate how the observed PdSn2 structure balances these effects by tuning the degree of Sn-Sn clustering and expansion of the Pd environment. These observations point to generalizations for most 18-n+m isomers, where increased main group ligand clustering (+m) and isolobal bonds (+n) can accommodate compositions with different T and E atomic sizes.

Promises and technological prospects of two-dimensional Rashba materials

The Rashba spin–orbit coupling effect, primarily arising from structural-inversion asymmetry in periodic crystals, has garnered considerable attention due to its tunability and potential applications in spintronics. Its capability to manipulate electron spin without an external magnetic field opens new avenues for spintronic device design, particularly in semiconductor technology. Within this framework, 2D Rashba materials hold special interest due to their inherent characteristics, which facilitate miniaturization and engineering capabilities. In this Perspective article, we provide an overview of recent advancements in the research of 2D Rashba materials, aiming to offer a comprehensive understanding of the diverse manifestations and multifaceted implications of the Rashba effect in material science. Rather than merely presenting a list of materials, our approach involves synthesizing various viewpoints, assessing current trends, and addressing challenges within the field. Our objective is to bridge the gap between fundamental research and practical applications by correlating each material with the necessary advancements required to translate theoretical concepts into tangible technologies. Furthermore, we highlight promising avenues for future research and development, drawing from insights gleaned from the current state of the field.

Structural phase transition of G-type antiferromagnetic SrMnO3 under pressure

Perovskite SrMnO3 is a versatile material with applications in transistors, supercapacitors, and spintronic devices. This study employs the DFT+U calculations to investigate the electronic and magnetic properties of two polymorphs: 4H-SrMnO3 and 3C-SrMnO3 under isotropic pressure conditions up to 60 GPa. A novel approach based on density functional perturbation theory (DFPT) is employed to precisely determine the on-site Hubbard U value, yielding a computed value of 4.552 eV, consistent with experimental reports. Below P = 14 GPa, the G-AFM phase of 4H-SrMnO3 is the most favored stable, and transitioning to the G-AFM phase of 3C-SrMnO3 beyond 14 GPa. Notably, we observed significant changes in the band gaps, exhibiting an increasing trend under isotropic pressure, while the magnetic moments of the Mn sites exhibit a decreasing trend from ≈2.8 μ B to ≈2.3 μ B for P = 0 GPa and 60 GPa, respectively. The projected density of states (PDOS) reveals the p-d hybridization contributions between the 3d-Mn and 2p-O covalent bonds, along with d-d Mott Hubbard interactions within the localized 3d orbitals of neighboring Mn-Mn atoms. Furthermore, a decrease in the Mn1-O-Mn2 distance prompts enhanced charge transfer which was facilitated by ligand holes, leading to a noticeable decrease in the magnetic moment of the Mn site in the G-AFM phase of SrMnO3.

A Visible Light-Responsive TiO2 Photocathode Achieved by a Rh Dopant.

Developing an efficient and stable photocathode material for photoelectrochemical solar water splitting remains challenging. Herein, we demonstrate the potential of rutile TiO2 as a photocathode by Rh doping with visible light absorption up to 640 nm and an onset potential of 0.9 V versus the reversible hydrogen electrode. The dopant transforms the rutile host from an n-type semiconductor to a p-type one, as confirmed by the Mott-Schottky curve and kelvin probe force microscopy. Physical and photoelectrochemical analyses further suggest that the doping mechanism is dependent on concentration. Lower levels of dopants generate localized Rh3+, while higher levels favor Rh4+ that interacts more strongly with the O 2p orbitals. The latter is found not only to extend the visible light absorption range but also to facilitate charge transport. This work elucidates the role of the Rh dopant in adjusting the photoelectrochemical behavior of TiO2, and it provides a promising photocathode material for solar energy conversion.

Precisely Constructing Orbital-Coupled Fe─Co Dual-atom Sites for High-Energy-Efficiency Zn-Air/Iodide Hybrid Batteries.

Rechargeable Zn-air batteries (ZABs) are promising for energy storage and conversion. However, the high charging voltage and low energy efficiency hinder their commercialization. Herein, these challenges are addressed by employing precisely constructed multifunctional Fe-Co diatomic site catalysts (FeCo-DACs) and integrating iodide/iodate redox into ZABs to create Zinc-air/iodide hybrid batteries (ZAIHBs) with highly efficient multifunctional catalyst. The strong coupling between the 3d orbitals of Fe and Co weakens the excessively strong binding strength between active sites and intermediates, enhancing the catalytic activities for oxygen reduction/evolution reaction and iodide/iodate redox. Consequently, FeCo-DACs exhibit outstanding bifunctional oxygen catalytic activity with a small potential gap (ΔE=0.66V) and outstanding stability. Moreover, an outstanding catalytic performance toward iodide/iodate redox is obtained. Therefore, FeCo-DAC-based ZAIHBs exhibit high energy efficiency of up to 75% at 10mAcm-2 and excellent cycling stability (72% after 500h). This research offers critical insights into the rational design of DACs and paves the way for high-energy efficiency energy storage devices.

Adsorption structure and properties of Ni/Fe electrodeposition interface: a DFT study

The density functional theory calculations of the adsorption model of NiCl2, Ni, and Cl on the Fe surface, as well as interface electronic properties, provide theoretical guidance for improving the Ni electrodeposition process. The adsorption properties of these three species on the Fe (100) crystal surface at different coverages, and the adsorption properties of the single Ni on three different crystal surfaces of Fe (100), Fe (110), and Fe (111), were studied through calculations of adsorption energy, charge density, charge occupancy, and DOS. The results indicate that the H sites are the most favorable for the adsorption of Ni and Cl on the Fe (100) surface. T sites, B sites, and H sites are all potential adsorption sites for NiCl2. The order of adsorption strength is Ni > Cl > NiCl2. In response to changes in charge, the adsorption effect exhibits a negative correlation with surface coverage. In addition, the hybridization of Ni’s 3d orbitals, Cl’s 3p orbitals, and Fe’s 3d orbitals changes the distribution of the interface charge, resulting in an increase of the charge in the Fe surface. Ni exhibits better adsorption performance on Fe (100) surface, driven by the lattice structure, surface electron configuration, and Ni–Fe atomic interactions.

Coexistence of Ferromagnetism and Superconductivity at KTaO3 Heterointerfaces.

The coexistence of superconductivity and ferromagnetism is a long-standing issue in superconductivity due to the antagonistic nature of these two ordered states. Experimentally identifying and characterizing novel heterointerface superconductors that coexist with magnetism presents significant challenges. Here, we report the observation of two-dimensional long-range ferromagnetic order in a KTaO3 heterointerface superconductor, showing the coexistence of superconductivity and ferromagnetism. Remarkably, our direct current superconducting quantum interference device measurements reveal an in-plane magnetization hysteresis loop persisting above room temperature. Moreover, first-principles calculations and X-ray magnetic circular dichroism measurements provide decisive insights into the origin of the observed robust ferromagnetism, attributing it to oxygen vacancies that localize electrons in nearby Ta 5d states. Our findings suggest KTaO3 heterointerfaces as time-reversal symmetry breaking superconductors, injecting fresh momentum into the exploration of the intricate interplay between superconductivity and magnetism enhanced by the strong spin-orbit coupling inherent to the heavy Ta in 5d orbitals.

First‐Principles Investigation of Electronic and Thermodynamic Properties of Honeycomb CuSe

AbstractIn the realm of materials science, a fascinating class of substances known as topological nodal line semimetals have garnered significant attention. These materials possess distinctive quantum states, characterized by topologically nontrivial conduction and valence bands that intricately intersect with the Fermi level. Such unique band structures give these materials a plethora of surprising properties, including the emergence of flat Landau levels and the appearance of long‐range Coulomb interactions. Notably, certain bulk materials, namely PbTaSe2, ZrSiS, PtSn4, and Cu2Si, exhibit these intriguing topological nodal lines. However, the theoretical investigation pertaining to CuSe and its Dirac nodal line properties remains relatively limited. In this work, we have employed simulations on CuSe to elucidate its distinctive physical properties such as a Dirac matter. There exist Dirac bands and band inversion in the vicinity of Fermi levels, and Fermi surface holds a Horn‐like structure. We pointed out the occurrence of mirror reflection symmetry‐protected Dirac nodal line fermions in copper selenide (CuSe) that make CuSe a candidate for Dirac nodal line fermion started by the Se 4p and Cu 3d orbitals. The nontrivial topological edge states further verify our proposal of the mirror reflection symmetry is broken by spin‐orbit coupling. These findings provide a new perspective that advances our comprehension of the remarkable properties exhibited by these materials, thereby paving the way for the development of high‐speed and low‐dissipation devices in the future.