Electrons Research Articles

Enhanced Energy Storage Properties for Bi(Ni0.5Hf0.5)O3 doped KNN Ceramics

Abstract In this work, (1-x)K0.5Na0.5NbO3-xBi(Ni0.5Hf0.5)O3 (x = 0.15, 0.17, 0.2, 0.25) [abbreviated by (1-x) KNN-xBNH] lead-free energy storage ceramics were prepared by the conventional solid-phase reaction method. The results indicate that BNH has been successfully incorporated into the KNN lattice, forming a homogeneous and stable solid solution. At the A site, hybridization between Bi 6p and O 2p orbitals can ameliorate the polarity, inducing an increase in Pmax. At the B site, Nb5+ is substituted by (Ni0.5Hf0.5)3+, leveraging differences in oxidation states and ionic radii to enhance the relaxation behavior. Moreover, the addition of BNH effectively refines grain size and optimizes breakdown field strength. At x = 0.17, the ceramics achieve optimal energy storage performance, with Wtot = 1.375 J/cm³, Wrec = 1.071 J/cm³, and η = 77.89%(~184 kV/cm).

Role of Fe-As banding in electronic structure of Co doped LiFeAs

Abstract Experiment shows that the maximum Co concentration of LiFeAs in the superconducting state is around 17%. First principles calculations show that the Fe-As bond length, c-axis length, and electronic structure change gently from 0% to 18% Co doping concentration, but suddenly undergo drastic changes at 20% Co doping. Unlike many 1111 and 122 type iron-based superconductors, the contribution of Fe 3p orbitals to N(EF) has significantly surpassed that of As 4p orbitals. The rapid decrease in N(EF) is associated with a sharp contraction of Fe-As bond, and Fe-As bond length has the ability to independently adjust N(EF). The sudden contraction of Fe-As bonds leads to a reverse Lifshitz transition in band, resulting in the fracture and severe shrinkage in the inner layer of the hole Fermi surface. The originally nested structure of the hole Fermi surfaces is destroyed, which may be the main reason for the termination of superconductivity.

Effects of spin–orbit coupling on tunnel magneto-resistance in resonant-tunneling magnetic tunnel junctions

Effects of spin–orbit coupling on tunnel magneto-resistance in resonant-tunneling magnetic tunnel junctions

Orbital Coupling of Dual-Atom Sites Boosts Electrocatalytic NO Oxidation and Dynamic Intracellular Response.

In situ measurement of nitric oxide (NO) in living tissue and single cells is highly important for achieving a profound comprehension of cellular functionalities and facilitating the precise diagnosis of critical diseases; however, the progress is greatly hindered by the weak affinity of ultratrace concentration NO in cellular environment toward electrocatalysts. Herein, a new strategy is reported for precisely constructing orbital coupled dual-atomic sites to enhance the affinity between the metal atomic sites and NO on a class of N-doped hollow carbon matrix dual-atomic sites Co─Ni (Co1Ni1-NC) for greatly boosting electrocatalytic NO performance. The as-synthesized Co1Ni1-NC demonstrates a substantially higher current density than Ni1-NC and Co1-NC, coupled with exceptional stability with a negligible degradation rate of 0.6 µA·cm-2·h-1, which is the best among the state-of-the-art electrocatalysts for NO oxidation. Experimental and theoretical investigations collectively reveal that the pivotal role of d-d orbit coupling between Co and Ni sites enables Ni to acquire additional electrons, leading to the occupation of Ni's 3dxy/yz within the 2π orbitals of NO, thus weakening the N≡O triple bond and concurrently accelerating NO adsorption kinetics. It is demonstrated that Co1Ni1-NC-coated nanoelectrode can achieve the in situ sensing of NO in living organs and single cells.

Phosphorus‐Tuned Nickel Boride Nanocatalyst with Enhanced p–p Interaction for Expediting Sulfur Electrochemistry in Lithium‐Sulfur Batteries

AbstractRationally modulating the electronic structure of sulfur electrocatalysts is essential for the development of reliable lithium–sulfur (Li–S) batteries. Herein, a phosphorus‐doping strategy is presented to finely tune the electronic properties of nickel boride (P‐NiB), facilitating highly efficient sulfur electrocatalysis. Through a combination of theoretical modeling and experimental validation, It is demonstrated that the electronegative P reduces the occupancy of B 2p orbitals, promoting B─S bonding via enhanced p‐p orbital interaction. Meanwhile, P and Ni atoms also exhibit strong affinities to polysulfides via p‐p and p‐d interactions, respectively, rendering a globally sulphophilic catalyst that effectively confines polysulfides and lowers conversion energy barriers. This leads to fast and durable sulfur redox reactions, with P‐NiB‐based Li–S cells outperforming their undoped NiB and bare carbon counterparts in both cyclability (1000 cycles) and rate capability (5 C). Furthermore, a high areal capacity of up to 8.94 mAh cm−2 is achieved under high‐loading and lean‐electrolyte conditions, along with the demonstration of a multi‐layered pouch cell delivering a high overall capacity of 1.2 Ah. This work highlights an efficient anion‐tuning strategy for optimizing metal boride‐based sulfur electrocatalysis, offering a promising pathway toward high‐performance and practically viable Li–S batteries.

Enhancing Reverse Intersystem Crossing with Extended Inverted Singlet–Triplet (X−INVEST) Systems

AbstractThe discovery of triangular‐shaped molecules displaying an inverted singlet–triplet (INVEST) energy gap between their lowest singlet (S1) and triplet (T1) states opened the way for a new strategy to increase the internal quantum efficiency (IQE) of organic light‐emitting diodes (OLEDs), enhancing the reverse intersystem crossing (RISC) thanks to a downhill process. However, the compounds showing a negative ΔEST suffer from both a vanishing spin–orbit coupling (SOC) between these excited states and high energy differences with higher‐lying singlets and triplets, therefore limiting their involvement in the spin conversion process. Here, we proposed a new design strategy entailing the extension of the triangulene cores by connecting two INVEST triangulene units to form Uthrene‐ and Zethrene‐like systems, doped with N and B. The inspection of the resulting molecular orbitals (MOs) distribution allowed rationalizing the electronic structure properties obtained from wavefunction‐based methods, showing how the Uthrene‐like architecture can lead to the quasi‐resonance between S1 and T1, in some cases provoking their inversion. By feeding a kinetic model with the non‐radiative rate constants, calculated from first principles, we showed how the extended INVEST (X−INVEST) design strategy can open new pathways to boost the spin conversion process and the population of the emissive S1.

Platinum Compound on Gold–Magnesia Hybrid Structure: A Theoretical Investigation on Adsorption, Hydrolysis, and Interaction with DNA Purine Bases

Cisplatin-based platinum compounds are important clinical chemotherapeutic agents that participate in most tumor chemotherapy regimens. Through density-functional theory calculations, the formation and stability of the inorganic oxide carrier, the mechanisms of the hydrolysis reaction of the activated platinum compound, and its binding mechanism with DNA bases can be studied. The higher the oxidation state of Pt (II to IV), the more electrons transfer from the magnesia–gold composite material to the platinum compound. After adsorption on the composite carrier, 5d←2p coordination bonds of Pt-N are strengthened. For flat and oblique adsorption modes of cisplatin, there is no significant difference in the density of states of the gold and magnesium oxide film, indicating the maintenance of the heterojunction structural framework. However, there are significant changes in the electronic states of cisplatin itself with different adsorption configurations. In the flat configuration, the band gap width of cisplatin is larger than that of the oblique configuration. The Cl-Pt bond range in the Pt(III) compound shows a clear charge reduction on the magnesia film, indicating the Cl-Pt bond is an active site with the potential for decomposition and hydrolysis. The substitution of chloride ions by water can lead to hydrolysis products, enhancing the polarization of the composite and showing strong charge separation. The hydrolysis of the free platinum compound is endothermic by 0.309 eV, exceeding the small activation energy barrier of 0.399 eV, indicating that hydrolysis of this platinum compound is easily achievable. ADME (absorption, distribution, metabolism, and excretion) prediction parameters indicate that hydrolysis products have good ESOL (Estimated SOLubility) solubility and high gastrointestinal absorption, consistent with Lipinski’s rule. During the coordination reaction process, there are significant changes in the distribution of frontier molecular orbitals, with the HOMO (highest occupied molecular orbital) of the initial state primarily located on the purine base, providing the possibility for electron transfer to the empty orbitals of the platinum compound in the LUMO (lowest unoccupied molecular orbital). The HOMO and HOMO-1 of the transition state and product are mainly distributed on the platinum compound, indicating clear electron transfer and orbital rearrangement. The activation energy barrier for the purine coordination reaction with the hydrolysis products is reduced to 0.61 eV, and the dipole moment gradually decreases to 6.77 Debye during the reaction, indicating a reduction in the system’s charge separation and polarization. This contribution is anticipated to provide a new theoretical clue for developing inorganic oxide carriers of platinum compounds.

Electronic and optical properties of a Ta2NiSe5 monolayer: A first-principles study

The crystal structure, stability, electronic, and optical properties of the Ta2NiSe5 monolayer have been investigated using first-principles calculations in combination with the Bethe–Salpeter equation. The results show that it is feasible to directly exfoliate a Ta2NiSe5 monolayer from the low-temperature monoclinic phase. The monolayer is stable and behaves as a normal narrow-gap semiconductor with neither spontaneous excitons nor non-trivial topology. Despite the quasi-particle and optical gaps of only 266 and 200 meV, respectively, its optically active exciton has a binding energy up to 66 meV and can exist at room temperature. This makes it valuable for applications in infrared photodetection, especially its inherent in-plane anisotropy adds to its value in polarization sensing. It is also found that the inclusion of spin–orbit coupling is theoretically necessary to properly elucidate the optical and excitonic properties of a monolayer.

Three-Dimensional Topological Semimetal/Insulator States in α-Type Organic Conductors with Interlayer Spin–Orbit Interaction

Three-Dimensional Topological Semimetal/Insulator States in <i>α</i>-Type Organic Conductors with Interlayer Spin–Orbit Interaction

Spin Hall magnetic field sensing device using topological insulator

The “direct” spin Hall (DSH) effect has been intensively studied to manipulate the magnetic state in spin–orbit torque magnetic random access memory. Meanwhile, its reciprocal phenomenon, known as the “inverse” spin Hall (ISH) effect, has been studied as a method to read the magnetic state of a magnetic element in a magnetic read head sensor and magnetoelectric spin–orbit logic device. This work studies a magnetic field sensing device structure in which the DSH effect is used for reading the magnetic state in a ferromagnetic (FM)/topological insulator (TI) heterostructure. We found that while the output of our DSH sensing device is consistent with that based on the ISH effect, the spin Hall angle calculated from its magnitude is colossal (θSH ∼ 164) and significantly higher than that (θSH ∼ 3.5) obtained from the second harmonic measurement. Our findings show that the giant DSH and ISH effects in TI-based heterostructures are useful for realizing next-generation magnetic read head device and have important implications for engineering topological quantum materials with high spin Hall performance.

Side‐Gate Modulation of Supercurrent in InSb Nanoflag‐Based Josephson Junctions

InSb nanoflags, due to their intrinsic spin–orbit interactions, are an interesting platform in the study of planar Josephson junctions. Ballistic transport, combined with high transparency of the superconductor/semiconductor interfaces, is reported to lead to interesting phenomena such as the Josephson diode effect. The versatility offered by the planar geometry can be exploited to manipulate both carrier concentration and spin–orbit strength by electrical means. Herein, experimental results on InSb nanoflag‐based Josephson junctions fabricated with side gates placed in close proximity to the junction are presented. It is shown that side gates can efficiently modulate the current through the junction, both in the dissipative and in dissipation‐less regimes, similar to what is obtained with a conventional back gate. Furthermore, the side gates can be used to influence the Fraunhofer interference pattern induced by the presence of an external out‐of‐plane magnetic field.

Spatial Conformation Engineering of Aromatic Ketones for Highly Efficient and Stable Perovskite Solar Cells.

Carbonyl-containing materials employed in state-of-the-art hybrid lead halide perovskite solar cells (PSCs) exhibit a strong structure-dependent electron donor effect that predominates in defect passivation. However, the impact of the molecular spatial conformation on the efficacy of carbonyl-containing passivators remains ambiguous, hindering the advancement of molecular design for passivating materials. Herein, we show that altering the spatial torsion angle of aromatic ketones from twisted to planar configurations, as seen in benzophenone (BP, 27.2°), anthrone (AR, 15.3°), and 9-fluorenone (FO, 0°), leads to a notable increment of the electron cloud density around the carbonyl group, thus improving the passivation ability for lead-based defects. Consequently, the PSC performance also relies on the torsion angle of the aromatic ketones, with the coplanar FO-based PSC achieving a highest power conversion efficiency (PCE) of 25.13% and retaining 92% of its initial efficiency after 1000 h of operation at the maximum power point under continuous 1-sun illumination (ISOS-L-1I). Moreover, a perovskite mini-module (14.0 cm2) containing FO exhibits a PCE of 20.19%. Our findings highlight the influence of molecular conformation on the passivation effect of the carbonyl group, offering deeper insight into the design and development of aromatic ketones as passivators for highly efficient and stable PSCs.

Floquet analysis on an irradiated nodal surface semimetal with non-symmorphic symmetry

A nodal surface semimetal (NSSM) features symmetry enforced band crossings along a surface within the three-dimensional (3D) Brillouin zone (BZ) and a presence of a nonsymmorphic symmetry there pushes such surfaces to stick to the BZ center or boundaries. The topological robustness of the same does not always come with nonzero Berry fluxes. We consider two such NS, one with zero and another with nonzero topological charges and investigate the effect of light irradiation on them. We find that depending on the state of polarization, one can obtain additional Weyl points/NS in the corresponding Floquet Hamiltonians. Particularly, using a simple two band spinless/spin polarized models with no spin orbit coupling, we emphasize the low energy behavior of the continuum Hamiltonians close to the band crossings and its evolution in a Floquet system in the high frequency limit. In the Floquet system, we also find the NS to perish or new multi Weyl points to get popped up for different polarization scenario or different NSSM Hamiltonians. Our findings open up important avenues on what out of equilibrium NSSM systems can offer in many active fields including quantum computations.

Electron-Lattice Synergistic Coordination for Boosting the Electro-Optic Response of the Crystal.

The electro-optic (E-O) response is fundamental where the refractive index of materials can be modulated by the external electric field. Up to now, E-O modulation has become a critical technology in photonics, quantum optics, modern communication, etc. However, the design of E-O crystals with broadband availabilities and large E-O effect is still challenging since the E-O response is contributed by both electrons and phonons. Here, an electron-lattice synergistic coordination strategy is proposed for boosting the E-O response, and with the langasite as the subject, a novel crystal La3Zr0.5Ga5Si0.5O14 (LZGS) is designed. By the rational introduction of the Zr4+ ion in the octahedral site, it is found that the E-O response can be obviously improved attributed to the active 4d orbitals of the Zr4+ ion and the optical phonons of the flexible (ZrO6) unit. This crystal also has advantages in transparency, laser damage threshold and E-O coefficient compared with the well-known E-O crystals. Moreover, broadband E-O modulation is also demonstrated in the lasers at wavelengths from 639 to 1991nm. These findings not only demonstrate an excellent E-O crystal for the development of modern devices in classical and quantum fields but also provide a design strategy for boosting the E-O response.

First-principles calculations of permalloy thin film on SrTiO3 substrate

Abstract The soft-magnetic permalloy is an iron-nickel alloy with high magnetic permeability and low coercivity, widely used in both high-frequency and low-frequency magnetic devices. This study investigates the property of permalloy thin films on SrTiO3 substrates using first-principles calculations, to simulate the heterojunction of permalloy and SrTiO3, and to compute the band structure and state density. The results show that on the permalloy–SrTiO3 interface, Fe atoms exhibit slight displacements, leading to in-plane contraction and out-of-plane expansion of the film. Additionally, the lattice mismatch induced by substrate stress is 2.0%, which is within the acceptable range. Analysis of the band structure and state density reveals that substrate stress significantly affects the magnetic properties of the permalloy thin film. It increases the state density near the Fermi level, and notably changes the magnetic moment. Further analysis indicates that the 3d orbitals of iron and nickel atoms contribute most to the magnetic moments, while the peak values of 3d-state density for iron and nickel atoms remain largely unchanged before and after stress. However, the spin density undergoes significant changes. These simulation results provide theoretical data support and reference for the application of permalloy thin films in high-performance magnetic devices.

Electronic Nature and Thermoelectric Characteristics of Cubic LaPb3 LaIn3 and LaTl3 Compounds: B3PW91 Approach

In this paper the structural, electronic and transport properties of the strongly correlated intermetallics LaX3 (X=Pb, In and Tl) in the space group Pm-3m (221) have been investigated using B3PW91 hybrid functional within the framework of density functional theory. These compounds have 4f orbitals and hence strong electron-electron correlation effect is expected, therefore, the electronic properties are also calculated with the B3PW91 hybrid functional and the effect of B3PW91 hybrid functional on the density of states is discussed in details. The band structure and density of states, demonstrate the metallic nature of these compounds. Using the semi-empirical Boltzmann’s approach implemented in the BoltzTraP code, the transport parameters, such as the Seebeck coefficient, electrical conductivity, thermal conductivity and figure of merit as a function of the chemical potential are computed at a temperature gradient of 500 K. For all materials the thermal and electrical conductivities, and Seebeck coefficient has higher values for n-type doping in comparison with p-type doping. The moderate values of figure of merit obtained for these materials indicate that these materials have applicability where small values of thermoelectric efficiency are required and higher values can harm the process but need experimental verification. LaIn3 has the highest value of electrical conductivity per relaxation time and thermal conductivity per relaxation time are 9.43 x 1020 1/Ωms and 107.65 x 1014 W/mKs respectively. LaTl3 has the highest figure of merit among these materials.

Atomistic Origins of Conductance Switching in an ε-Cu0.9V2O5 Neuromorphic Single Crystal Oscillator.

Building artificial neurons and synapses is key to achieving the promise of energy efficiency and acceleration envisioned for brain-inspired information processing. Emulating the spiking behavior of biological neurons in physical materials requires precise programming of conductance nonlinearities. Strong correlated solid-state compounds exhibit pronounced nonlinearities such as metal-insulator transitions arising from dynamic electron-electron and electron-lattice interactions. However, a detailed understanding of atomic rearrangements and their implications for electronic structure remains obscure. In this work, we unveil discontinuous conductance switching from an antiferromagnetic insulator to a paramagnetic metal in ε-Cu0.9V2O5. Distinctively, fashioning nonlinear dynamical oscillators from entire millimeter-sized crystals allows us to map the structural transformations underpinning conductance switching at an atomistic scale using single-crystal X-ray diffraction. We observe superlattice ordering of Cu ions between [V4O10] layers at low temperatures, a direct result of interchain Cu-ion migration and intrachain reorganization. The resulting charge and spin ordering along the vanadium oxide framework stabilizes an insulating state. Using X-ray absorption and emission spectroscopies, assigned with the aid of electronic structure calculations and measurements of partially and completely decuprated samples, we find that Cu 3d and V 3d orbitals are closely overlapped near the Fermi level. The filling and overlap of these states, specifically the narrowing/broadening of V 3dxy states near the Fermi level, mediate conductance switching upon Cu-ion rearrangement. Understanding the mechanisms of conductance nonlinearities in terms of ion motion along specific trajectories can enable the atomistic design of neuromorphic active elements through strategies such as cointercalation and site-selective modification.

Correlating Double‐Cone Polariton Dynamics with Local Femtosecond Laser Modifications in Ultrashort‐Pulse‐Stimulated Crystals

AbstractStrong similarities for relativistic electrons stimulated from electron beams and electron clouds are merging the boundary of wave‐particle duality of electrons, one of which being superposition is Cherenkov radiations. Recent theoretical investigations into quantum Cherenkov effects for cone‐shape particles have hypothesized electron‐spin flip transitions in bound‐ and free‐electron systems like bulk silica and graphene. However, experimental validation of these predictions remains outstanding. Here, analogous phenomena of polariton‐version quantum Cherenkov radiations observed by broadband femtosecond pump‐probe experiments is reported, and demonstrate double‐cone emission processes involving of Cherenkov‐type phonon polaritons (PhPs) and plasmon‐PhPs in ultrashort‐pulse‐stimulated ferroelectric crystals and graphene, respectively. Through component analysis of double‐cone polariton emissions using an empirical quantum dynamics model, the initial polariton dynamics are restored by time translation corrections. The resulting quantum wave packets of PhPs are found to be correlated with femtosecond‐laser‐induced modifications inside ferroelectric lithium niobates, achieving a PhP threshold criterion for ultrasmooth femtosecond laser nanofabrication.

Study of phase decoherence in GeSn (8%) through measurements of the weak antilocalization effect

Alloying germanium with tin offers a means to modulate germanium's electronic structure, enabling a greater degree of control over quantum properties such as the retention of the phase or spin of the electron wave. However, the extent to which the presence of high dopant concentrations in GeSn alters these quantum behaviors is poorly understood. Here, we investigate the role of dopant concentrations on phase coherence through measurements of the weak antilocalization (WAL) effect at temperatures between 30 mK and 10 K in p-GeSn (8%) thin films, which were doped to a series of carrier densities on the order of 1012cm−2. Phase coherence and spin–orbit lengths were extracted from the magnetoconductivities using the 2D Hikami–Larkin–Nagaoka model. Phase coherence lengths peaked at 577, 593, and 737nm for the low-, mid-, and high-density samples, while upper limits on the spin–orbit lengths of less than 25nm were relatively independent of carrier density and temperature. The phase coherence lengths increased as the temperature decreased but changed only minimally with carrier density, contrary to common models of temperature-dependent inelastic scattering. Saturation of the phase coherence lengths occurred below 600mK. Based on these findings, intrinsically generated inelastic scattering mechanisms such as two-level systems or impurity band scattering likely contribute to phase decoherence in these alloys. Our results provide insight into the inelastic scattering mechanisms of GeSn, while suggesting a need for further investigation into phase decoherence mechanisms in doped group-IV alloys.

Enhanced perpendicular magnetic anisotropy energy and Curie temperature in the CrOCl monolayer: strain effects

Abstract Magnetic monolayers offer a wide variety of applications in enhancing the functionalities of storage devices including higher thermal stability, lower power consumption, and higher operation speed, owing to their intrinsic long-range spin ordering. Herein, we study the biaxial ([110]) strain range of ± 5% influence on the formation energetics, electronic structure, and magnetic behaviour of the CrOCl monolayer (ML) based on the ab-initio calculations including spin–orbit coupling (SOC) effects. It is predicted that the system displays an insulating character having an energy band gap (E g ) of 2.05 eV with a ferromagnetic (FM) ground state in its unstrained state. The estimated partial spin magnetic moment on the Cr ion is +2.7 μ B /f.u. (per formula unit) with S = 1.5 and lies in a + 3 oxidation state with an electronic distribution of t 2 g 3 ↑ t 2 g 0 ↓ e g 0 ↑ e g 0 ↓ . Along with this, [001] (c-axis) is found to be the easy magnetic axis, which results in a magnetic anisotropy energy (MAE) of 0.2 meV having an MAE constant of 0.25 mJ m−2 and the computed Curie temperature (T c ) using Ising model is 157 K. Furthermore, the system shows the robustness of the FM insulating behavior against considered strains. However, a significant shift in the conduction band edge (CBE) position to lower energies is evident for tensile strains, which substantially reduces the E g up to 13%. The decrease in E g value is evidence of higher absorption in the visible range which makes it the best option for optoelectronics and photocatalysis. Simultaneously, our results revealed that strain enhances the MAE and T c up to 190% and 43%, respectively. Hence, optimized E g , MAE, and T c within a considerable strain range, make the CrOCl ML a potential candidate for its utilization in magnetic memory devices.