Browse Articles

Valley polarization in two-dimensional zero-net-magnetization magnets

Valleytronics in two-dimensional (2D) zero-net-magnetization magnets exhibits ultradense and ultrafast potential due to their intrinsic advantages of zero stray field and terahertz dynamics. The zero-net-magnetization magnets mainly include PT-antiferromagnet [the joint symmetry (PT) of space inversion symmetry (P) and time-reversal symmetry (T)], altermagnet, and fully compensated ferrimagnet. In these magnets, achieving controllable valley polarization is extremely important to the application of valleytronics. In this perspective article, we provide some possible design strategies to achieve valley polarization and spin-splitting in 2D zero-net-magnetization magnets. Furthermore, the anomalous valley Hall effect can be achieved in these zero-net-magnetization magnets. These proposed design strategies can encourage more theoretical and experimental works to explore valley polarization in these eminent magnets.

Tunable sliding ferroelectricity in two-dimensional van der Waals RuX2 (X = Cl, Br, and I) multiferroic layers

Two-dimensional (2D) van der Waals (vdW) materials offer vast potential for designing ferroelectrics with desired properties through simple layer stacking. Here, based on first principles, we demonstrate that the vdW layered crystals RuX2 (X = Cl, Br, and I) are a class of 2D multiferroic sliding ferroelectrics. The stacking of two magnetic RuX2 monolayers with the same orientation breaks the spatial inversion symmetry, resulting in a stable vertical polarization. In addition, the direction of polarization can be reversed through slight interlayer sliding, in which it only needs to overcome the small energy barrier of 7.16 meV. Among these layered crystals, the bilayer RuI2 not only possesses a remarkable sliding ferroelectricity of 0.49 pC/m but also exhibits stable long-range magnetic order due to its large magnetic anisotropy energy. When the RuI2 stack is increased to trilayers, the polarization significantly increases to 1.03 pC/m, which is much larger than that of its bilayer structure. Furthermore, the application of compressive strain results in a substantial increase in vertical polarization. This work provides an efficient method for designing 2D multiferroic sliding ferroelectric materials by stack engineering.

Band engineering for large perpendicular magnetocrystalline anisotropy and low magnetic Gilbert damping constant by anion substitution at Fe/MgO interface

Large interfacial perpendicular magnetocrystalline anisotropy (iPMA) and low Gilbert magnetic damping constant (α) in magnetic tunnel junctions (MTJs) are desired to achieve higher storage density and lower standby power operations in magnetic random-access memory. This work theoretically investigates effects of nitrogen and fluoride anions (N-anion and F-anion) substitution on the MgO barrier interface of Fe/MgO/Fe MTJ for iPMA and α using first-principles calculations. We find that the N-anion substitution significantly enhances iPMA by four times and reduces α by 65% compared to the pristine Fe/MgO/Fe, indicating a guideline toward an MTJ with large iPMA and low α simultaneously. The mechanism is explained by a band realignment at the Fermi level (EF) where Fe d±1 (dxz,dyz) orbitals at the interface are pushed above and below EF but Fe d±2 (dxy, dx2−y2) orbitals remain at EF by the N-anion substitution.

Efficient quantum frequency conversion of ultra-violet single photons from a trapped ytterbium ion

Ion trap system is a leading candidate for quantum information science benefitting from its long coherence time, high-fidelity gate operations. In addition, the ion photon entanglement provides a versatile tool to realize quantum networks by generating an ideal pair of a stationary memory qubit and a flying communication qubit. Rapid developments in nonlinear quantum frequency conversion techniques have enhanced the potential for constructing a trapped ion quantum network via optical fiber connections. The generation of long-distance entanglement has been demonstrated with ions such as Ca+ and Ba+, which emit photons in visible or near-infrared range naturally. On the other hand, as the qubit-native photons reside in ultra-violet (UV) spectrum, the Yb+ ion has not been considered as a strong competitor for telecommunication qubits despite extensive research on it. Here, we demonstrate an efficient difference-frequency conversion of UV photons, emitted from a trapped Yb+ ion, into a visible range. We provide experimental evidence that confirms the converted photons are radiated from the Yb+ ion. Our results provide a crucial step toward realizing a long-distance trapped ion quantum network based on Yb+ ions through quantum frequency conversion.

Optical absorption stacking modulation in atypical multilayer graphene

With graphene layers increasing, the interlayer charge transfers would generate an out-of-plane electric dipole moment, which is directly related to the optical absorption according to the Fermi Golden rule. Thus, in this work, we investigated the relationship between the absorption of multilayer graphene with different stacking orders from the transition dipole moment (TDM) and joint density of states (JDOS). It is found that the interlayer linkage of different stacking sequences leads to the varied chiral pseudospin doublets, which results in changes in TDM, consequently influencing the absorption spectra in the infrared and visible regions. While the enhanced absorption in the thicker multilayers from the ultraviolet to ionizing radiation region could be attributed to the increasement of JDOS. The comprehensive understanding of the absorption mechanism behind the multilayer graphene could provide another way of thinking about the optical absorption stacking modulation in atypical multilayer graphene.

Growth of nitrogen-doped (010) <i>β</i>-Ga2O3 by plasma-assisted molecular beam epitaxy using an O2/N2 gas mixture

In this study, we report on the intentional nitrogen doping of plasma-assisted MBE (PAMBE)-grown (010) β-Ga2O3 films by generating the growth plasma with an O2 and N2 gas mixture. A nitrogen doping range of 1.3 × 1018 to 4.5 × 1019 cm−3 was achieved. The nitrogen doping profiles have top-hat shapes with sharp turn-on and turn-off. Nitrogen doping was found to have a negligible impact on surface morphology. Nitrogen incorporation was unaffected by gallium flux and growth temperatures over a large growth window. An incorporation dependence on plasma power and total gas flow rate was observed. This was attributed to the N2 triple bond strength compared to the O2 double bond strength, which makes N2 harder to crack in the plasma source. Increasing the plasma power from 140 to 230 W increased nitrogen incorporation by 1.6×, while increasing the total gas flow rate from 0.8 to 2.0 sccm decreased incorporation by 3.2×. The compensation effect of nitrogen was verified by characterizing effective carrier concentration in conducting tin and nitrogen co-doped films. A 2.1 V built-in voltage was extracted from a nitrogen-doped, n− junction device using CV measurements. The device was found to exhibit rectifying behavior with a 100 A/cm2 current density at 2.9 V. The junction demonstrated here can play a key role in field management and electrostatic engineering for β-Ga2O3-based power devices. Overall, the controllability of PAMBE nitrogen doping and the properties of nitrogen-doped films suggest PAMBE-grown, nitrogen-doped layers have promising power device applications.

Aberration measurement by electron ptychography and consistency among different algorithms

Control over and knowledge of the electron probe is important in all scanning transmission electron microscopy (STEM) techniques. This is emphasized especially in electron ptychography, where the accurate probe wave function is required to deconvolve illumination from the specimen. The majority of ptychographic algorithms, such as the extended ptychographic iterative engine, reconstruct the electron probe on a pixelated grid numerically self-consistently. Solutions are thus not necessarily bound to wave functions physically realizable by the optical system. A method is presented to characterize reconstructed probes by conventional lens aberrations. The fitted aberrations are then used to investigate the quality of the retrieved probes, and their consistency is examined in a systematic study using a 4D-STEM focal series recorded for a thin SnS2 2D flake. Additionally, the influences of partial coherence and limited electron dose on the retrieved probes are analyzed, and the usefulness of the retrieved probes for different ptychographic methods, such as single sideband, Wigner distribution deconvolution ptychography, and gradient descent-based schemes, is elucidated. Finally, applications for ptychography-driven alignments of aberration-correcting electron optics are outlined.

High-frequency/high-field electron paramagnetic resonance generalized spectroscopic ellipsometry characterization of Cr3<b>+</b> in <b> <i>β</i> </b>-Ga2O3

Electron paramagnetic resonance of Cr3+ ions in β-Ga2O3 is investigated using terahertz spectroscopic ellipsometry under magnetic field sweeping, a technique that enables the polarization resolving capabilities of ellipsometry for magnetic resonance measurements. We employed a single-crystal chromium-doped β-Ga2O3 sample, grown by the Czochralski method, and performed ellipsometry measurements at magnetic field strengths ranging from 2 to 8 T, at frequencies from 82 to 125 and 190 to 230 GHz, and at a temperature of 15 K. Analysis of the frequency-field diagrams derived from all Mueller matrix elements allowed us to differentiate between the effects of electron spin Zeeman splitting and zero-field splitting and to accurately determine the anisotropic Zeeman splitting g-tensor and the zero-field splitting parameters. Our results confirm that Cr3+ ions predominantly substitute into octahedral gallium sites. Line shape analysis of Mueller matrix element spectra using the Bloch–Brillouin model provides the spin volume concentration of Cr3+ sites, showing very good agreement with results from chemical analysis by inductively coupled plasma-optical emission spectroscopy and suggesting minimal occupation of sites with inactive electron paramagnetic resonance. This study enhances our understanding of the magnetic and electronic properties of chromium-doped β-Ga2O3 and demonstrates the effectiveness of high-frequency/high-field electron paramagnetic resonance generalized spectroscopic ellipsometry for characterizing defects in ultrawide-bandgap semiconductors.

Elegant high-order harmonic vortices generation

High-order harmonic generation is a cornerstone of attosecond science, with applications spanning from spectroscopy to the creation of ultrashort light pulses with temporal duration falling in the attosecond regime. In addition, light beams carrying orbital angular momentum (OAM) allow studies of light–matter interactions mediated by OAM couplings. In this work, we present an alternative approach to generating high-order harmonic vortices using elegant Laguerre–Gaussian (eLG) beams. We examine the spatiotemporal characteristics of these harmonic vortices in the far-field regime and demonstrate how the low divergence of eLG beams makes them suitable for producing extreme ultraviolet (XUV) twisted attosecond pulses. Additionally, by solving the far-field Fraunhofer integral, we analyze the influence of azimuthal and radial indices on the spatial profile of vortex beams, thereby exploring the impact of larger topological charges. This study extends the concept of harmonic vortices generated by Laguerre–Gaussian beams to applications beyond the paraxial approximation.

A site-selection multi-element co-doping strategy in three-layered bismuth-based layered perovskite-like structure ferroelectrics leads to large energy storage capability

Improving the energy storage density of dielectric capacitors, which are widely used in power electronic devices, is a continuous challenge. In this work, a site-selection multi-element co-doping strategy was used by doping Pr atoms at the A-site and then doping Mn atoms at the B-site in bismuth-based layered perovskite-like structure prototype ferroelectrics Bi4Ti3O12 due to its large polarization and high Curie temperature. On the one hand, the substitution of Bi3+ with Pr3+ at the A-site introduces significant cation disorder, which disrupts the long-range ferroelectric order, consequently leading to a reduction in remnant polarization. On the other hand, the substitution of Ti4+ by Mn4+ at the B-site results in delayed polarization saturation due to the different electronic configurations between d3 Mn4+ and d0 Ti4+. In addition, the leakage current of the thin film exhibits a continuous decrease with doping concentration, which can be attributed to microstructural modifications including reduced grain size and the formation of amorphous regions, consequently leading to an enhanced breakdown field. Finally, a recoverable energy storage density of 42.1 J cm−3 and an efficiency of 69.9% were obtained for the BPT film, and a recoverable energy storage density of 81.8 J cm−3 and an efficiency of 73% were achieved in the BPTM film. The enhanced energy storage density can be attributed to the synergistic effect of co-doping of A- and B-sites on polarization and breakdown. Besides, the doped films have excellent frequency, temperature, and cycling stability. This work provides a guide to substantially enhance dielectric energy storage by a site-selection multi-element co-doping strategy.

Ultrafast 0D/1D ZnO/CuO photodetector in nanosecond scale by engineering the type-II heterostructure

Zero-dimensional/one-dimensional (0D/1D) heterojunctions have excellent potential in the field of optoelectronic devices due to the synergy effect of different dimensions. Most reported 0D/1D heterojunction photodetectors only focus on optimizing the separation efficiency of photogenerated carriers at the interface. However, the carriers within the quantum dots (QDs) cannot be transferred to the electrodes, resulting in recombination of photogenerated carriers separated at the interface. Therefore, the response speed of most 0D/1D heterojunction photodetectors is still limited to the order of seconds (s) and milliseconds (ms). In our work, we demonstrate a nanosecond (ns) scale ZnO/CuO heterojunction photodetector with efficient photoelectric conversion by engineering the type-II 0D/1D heterojunction interface. Herein, the surface defect states of ZnO QDs are deliberately introduced as “electrons storage pool” to suppress carrier recombination and further promote separation, which has been confirmed by photoluminescence (PL) and time-resolved photoluminescence (TRPL). As a result, the photodetector exhibited excellent performance with ultrafast response speed of 20 ns, responsivity of 213 A/W, and detectivity of 2.95 × 1011 Jones, respectively. This defect related interface engineering provides a feasible strategy for the development of high-performance 0D/1D heterojunction photodetectors.

Multi-band nonreciprocal thermal radiation based on Weyl semimetals with epsilon-near-zero multilayers

Although various nonreciprocal thermal emitters have been suggested to break the balance between absorption and emission, few structures can achieve strong nonreciprocity in more than three bands. To break this constraint, we propose a nonreciprocal thermal emitter device based on GaN/AIN/SiC/Weyl semimetal (WSM), which is capable of three discrete pairs of near-perfect absorption and emission, leading to perfect hexa-band strong nonreciprocal radiation. The enhanced nonreciprocal thermal radiation is attributed to the field enhancement of epsilon-near-zero layer and nonreciprocal guided resonances excited in the WSM film. By studying the magnetic field distribution, the physical mechanism of multi-band nonreciprocal thermal radiation is revealed, which can be verified by the impedance matching theory. Furthermore, the dependence of the structure dimensions and the axial vector b of the Weyl semimetal on the performance of the nonreciprocal radiation is investigated in detail. We believe that this work can provide an approach to the development of energy conversion devices and frequency selective detectors.

Characterizing self-heating dynamics using cyclostationary measurements

Self-heating in surround gate (e.g., nanosheet, nanowire, and FinFET) transistors degrades their on-current performance and reduces their lifetime. If a transistor heats/cools with time constants much shorter than the inverse of the operating frequency, predictable, frequency-independent performance is expected; if not, the operating frequency must be optimized for the highest performance. Typically, time constants are measured by expensive, ultra-fast instruments with high temporal resolution. Instead, here, we demonstrate an alternate, inexpensive, cyclostationary measurement technique to characterize self-heating (and cooling) with sub-microsecond resolution. The results are independently confirmed by direct imaging of the transient heating/cooling of the channel temperature by the thermoreflectance method. Routine use of the proposed technique will help improve the design of the surrounding gate transistors and shorten their design cycle.

Dual-branch image projection network for geographic atrophy segmentation in retinal OCT images

Plasmodium falciparum Pfs47 haplotype compatibility to Anopheles gambiae in Kisumu, a malaria-endemic region of Kenya

Abstract Insecticide resistance and outdoor transmission have reduced the effectiveness of existing malaria transmission prevention strategies. As a result, targeted approaches to support continuing malaria control, such as transmission-blocking vaccines, are required. Cross-sectional mass blood screening in children between 5 and 15 years was conducted in Chulaimbo, Kisumu, during the dry and wet seasons in 2018 and 2019. Plasmodium falciparum gametocyte carriers were identified by Microscopy. Subsequently, carriers were used to feed colony bred Anopheles gambiae females in serum replacement and whole blood membrane feeding experiments. The infection prevalence was 19.7% (95% Cl 0.003–0.007) with 95% of the infections being caused by P. falciparum . Of all confirmed P. falciparum infections, 16.9% were gametocytes. Thirty-seven paired experiments showed infection rates of 0.9% and 0.5% in the serum replacement and whole blood experiments, respectively, with no significant difference (P = 0.738). Six Pfs47 haplotypes were identified from 24 sequenced infectious blood samples: Hap_1 (E27D and L240I), Hap_2 (S98T); Hap_3 (E27D); Hap_4 (L240I); Hap_5 (E188D); and Hap_6 without mutations. Haplotype 4 had the highest frequency of 29.2% followed by Hap_3 and Hap_6 at 20.8% each then Hap_1 with a frequency of 16.7%, whereas Hap_5 and Hap_2 had frequencies of 8.3% and 4.2% respectively. Varying frequencies of Pfs47 haplotypes observed from genetically heterogeneous parasite populations in endemic regions illuminates vector compatibility to refracting P. falciparum using the hypothesized lock and key analogy. This acts as a bottleneck that increases the frequency of P. falciparum haplotypes that escape elimination by vector immune responses. The interaction can be used as a potential target for transmission blocking through a refractory host.

Risk factors for pterygium recurrence based on a retrospective study of 196 patients

Association of cholecystectomy with short-term and long-term risks of depression and suicide

Pathophysiological link between carotid atherosclerosis and cerebral white matter lesions

Mitigating doxorubicin-induced hepatotoxicity in male rats: The role of aerobic interval training and curcumin supplementation in reducing oxidative stress, endoplasmic reticulum stress and apoptosis

Characterization of the electronic structure and fate of doubly ionized carbon diselenide

Abstract Single photon double ionization of carbon diselenide ( $${\hbox {CSe}}_{2}$$ ) has been investigated by means of multi-particle coincidence techniques. The interpretation of the experimental spectra is helped by post-Hartree-Fock computations at the Coupled Clusters and Multi-Reference Configuration-Interaction levels to determine the energetics and electronic state potentials of $$\hbox {CSe}_2^{2+}$$ and its fragments. The lowest experimental double ionization energy of $${\hbox {CSe}}_{2}$$ has been found to be 24.68 ± 0.20 eV, reflecting the $$\hbox { X} ^3\Sigma ^-_g$$ ground state, and is in agreement with the theoretical vertical double ionization energy of 24.41 eV. Several fragmentation channels are reported including experimental appearance energies and kinetic energy releases in comparison to theoretical results on their characteristics. In particular, we identify several purely repulsive, Coulomb explosion fragmentation channels.