Topological Dirac semimetals (DSMs) present a kind of topologically nontrivial quantum state of matter, which has massless Dirac fermions in the bulk and topologically protected states on certain surfaces. In superconducting DSMs, the effects of their nontrivial topology on superconducting pairing could realize topological superconductivity in the bulk or on the surface. As superconducting pairing takes place at the Fermi level E_F, to make the effects possible, the Dirac points should lie in the vicinity of E_F so that the topological electronic states can participate in the superconducting paring. Here, we show using angle-resolved photoelectron spectroscopy that in a series of (Ir_1-xPt_x)Te₂ compounds, the type-Ⅱ Dirac points reside around E_F in the superconducting region, in which the bulk superconductivity has a maximum T_c of~3 K. The realization of the coexistence of bulk superconductivity and low-energy Dirac fermions in (Ir_1-xPt_x)Te₂ paves the way for studying the effects of the nontrivial topology in DSMs on the superconducting state.

We have investigated the flux symmetry on the capsule in a six-cylinder-port hohlraum for improving the design of the hohlraum. The influence factors of drive symmetry on the capsule in the hohlraum are studied, including laser power, laser beams arrangement, hohlraum geometric parameters, plasma condition, capsule convergence, etc. The x-ray radiation flux distribution on the capsule is obtained based on the three-dimensional view factor model. In the six-cylinder-port hohlraum, the main drive asymmetry is the C₄₀ mode asymmetry. When the C₄₀ mode asymmetry approaches zero, the drive symmetry on the capsule is optimal. Our results demonstrate that in order to have a high flux symmetry on the capsule in the laser main-pulse stage, more negative initial C₄₀ modes are needed, which can be realized by adjusting the hohlraum geometry parameters. The hohlraum with column length L_H=4.81 mm has an optimal symmetry in the laser main-pulse stage.

The structural phase transitions of bismuth under rapid compression has been investigated in a dynamic diamond anvil cell using time-resolved synchrotron x-ray diffraction. As the pressure increases, the transformations from phase I, to phase Ⅱ, to phase Ⅲ, and then to phase V have been observed under different compression rates at 300 K. Compared with static compression results, no new phase transition sequence appears under rapid compression at compression rate from 0.20 GPa/s to 183.8 GPa/s. However, during the process across the transition from phase Ⅲ to phase V, the volume fraction of product phase as a function of pressure can be well fitted by a compression-rate-dependent sigmoidal curve. The resulting parameters indicate that the activation energy related to this phase transition, as well as the onset transition pressure, shows a compression-rate-dependent performance. A strong dependence of over-pressurization on compression rate occurs under rapid compression. A formula for over-pressure has been proposed, which can be used to quantify the over-pressurization.

We study the phase diagram of the interacting fermionic two-leg ladder, which is featured by pair hopping and interactions of singlet and triplet superconducting channels. By using Abelian bosonization method, we obtain the full phase diagram of our model. The superconducting triplet pairing phase is characterized by a fractional edge spin and interpreted as two Kitaev chains under the mean filed approximation. The pair hopping will give rise to spin-density-wave (SDW) orders and can also support Majorana edge modes in spin channel. At half filling, the resulting Majorana-SDW phase shows additional fractionalization in charge channel, and can be interpreted as two Su-Schrieffer-Heeger (SSH) chains in the mean field regime.

The multiferroicity in the RMn₂O₅ family remains unclear, and less attention has been paid to its dependence on high-temperature (high-T) polarized configuration. Moreover, no consensus on the high-T space group symmetry has been reached so far. In view of this consideration, one may argue that the multiferroicity of RMn₂O₅ in the low-T range depends on the poling sequence starting far above the multiferroic ordering temperature. In this work, we investigate in detail the variation of magnetically induced electric polarization in GdMn₂O₅ and its dependence on electric field poling routine in the high-T range. It is revealed that the multiferroicity does exhibit qualitatively different behaviors if the high-T poling routine changes, indicating the close correlation with the possible high-T polarized state. These emergent phenomena may be qualitatively explained by the co-existence of two low-T polarization components, a scenario that was proposed earlier. One is the component associated with the Mn³⁺-Mn⁴⁺-Mn³⁺ exchange striction that seems to be tightly clamped by the high-T polarized state, and the other is the component associated with the Gd³⁺-Mn⁴⁺-Gd³⁺ exchange striction that is free of the clamping. The present findings may offer a different scheme for the electric control of the multiferroicity in RMn₂O₅.

The goal of this study is to analyze the statistics of the backscatter signal from bovine cancellous bone using a Nakagami model and to evaluate the feasibility of Nakagami-model parameters for cancellous bone characterization. Ultrasonic backscatter measurements were performed on 24 bovine cancellous bone specimens in vitro and the backscatter signals were compensated for the frequency-dependent attenuation prior to the envelope detection. The statistics of the backscatter envelope were modeled using the Nakagami distribution. Our results reveal that the backscatter envelope mainly followed pre-Rayleigh distributions, and the deviations of the backscatter envelope from Rayleigh distribution decreased with increasing bone density. The Nakagami shape parameter (i.e., m) was significantly correlated with bone densities (R=0.78-0.81, p<0.001) and trabecular microstructures (|R|=0.46-0.78, p<0.05). The scale parameter (i.e., Ω) and signal-to-noise ratio (SNR) also yielded significant correlations with bone density and structural features. Multiple linear regressions showed that bone volume fraction (BV/TV) was the main predictor of the Nakagami parameters, and microstructure produced significantly independent contribution to the prediction of Nakagami distribution parameters, explaining an additional 10.2% of the variance at most. The in vitro study showed that statistical parameters derived with Nakagami model might be useful for cancellous bone characterization, and statistical analysis has potential for ultrasonic backscatter bone evaluation.

This paper reports the sensitive effect of photoluminescence peak intensity and transmittance affected by B, Al, and N dopants in fluorescent 4H-SiC single crystals. The crystalline type, doping concentration, photoluminescence spectra, and transmission spectra were characterized at room temperature. It is found that the doped 4H-SiC single crystal emits a warm white light covering a wide range from 460 nm to 720 nm, and the transmittance increases from ~10% to ~60% with the fluctuation of B, Al, and N ternary dopants. With a parameter of C_D-A, defined by B, Al, and N concentration, the photoluminescence and transmittance properties can be adjusted by optimal doping regulation.

Synapse emulation is very important for realizing neuromorphic computing, which could overcome the energy and throughput limitations of today's computing architectures. Memristors have been extensively studied for using in nonvolatile memory storage and neuromorphic computing. In this paper, we report the fabrication of vertical sandwiched memristor device using ultrathin quasi-two-dimensional gallium oxide produced by squeegee method. The as-fabricated two-terminal memristor device exhibited the essential functions of biological synapses, such as depression and potentiation of synaptic weight, transition from short time memory to long time memory, spike-timing-dependent plasticity, and spike-rate-dependent plasticity. The synaptic weight of the memristor could be tuned by the applied voltage pulse, number, width, and frequency. We believe that the injection of the top Ag cations should play a significant role for the memristor phenomenon. The ultrathin of medium layer represents an advance to integration in vertical direction for future applications and our results provide an alternative way to fabricate synaptic devices.

InGaSb/AlGaAsSb double-quantum-well diode lasers emitting around 2 μm are demonstrated. The AlGaAsSb barriers of the lasers are grown with digital alloy techniques consisting of binary AlSb/AlAs/GaSb short-period pairs. Peak power conversion efficiency of 26% and an efficiency higher than 16% at 1 W are achieved at continuous-wave operation for a 2-mm-long and 100-μm-wide stripe laser. The maximum output power of a single emitter reaches to 1.4 W at 7 A. 19-emitter bars with maximum efficiency higher than 20% and maximum power of 16 W are fabricated. Lasers with the short-period-pair barriers are proved to have improved temperature properties and wavelength stabilities. The characteristic temperature (T₀) is up to 140℃ near room temperature (25-55℃).

Among all-solid-state batteries, rechargeable Al-ion batteries have attracted most attention because they involve three-electron-redox reactions with high theoretic specific capacity. However, the solid Al-ion conductor electrolytes are less studied. Here, the microscopic path of Al³⁺-ion conduction of NASICON-type (Al_0.2Zr_0.8)_20/19Nb(PO₄)₃ oxide is identified by temperature-dependent neutron powder diffraction and aberration-corrected scanning transmission electron microscopy experiments. (Al_0.2Zr_0.8)_20/19Nb(PO₄)₃ shows a rhombohedral structure consisting of a framework of (Zr,Nb)O₆ octahedra sharing corners with (PO₄) tetrahedra; the Al occupy trigonal antiprisms exhibiting extremely large displacement factors. This suggests a strong displacement of Al ions along the c axis of the unit cell as they diffuse across the structure by a vacancy mechanism. Negative thermal expansion behavior is also identified along a and b axes, due to folding of the framework as temperature increases.

The temporal response of cadmium-zinc-telluride (CZT) crystals is evaluated at room temperature by using an ultrafast-pulsed x-ray source. The dynamics of carrier relaxation in a CZT single crystal is modeled at a microscopic level based on a multi-trapping effect. The effects of the irradiation flux and bias voltage on the amplitude and full width at half maximum (FWHM) of the transient currents are investigated. It is demonstrated that the temporal response process is affected by defect level occupation fraction. A fast photon current can be achieved under intense pulsed x-ray irradiation to be up to 2.78×10⁹ photons mm^-2·s^-1. Meanwhile, it is found that high bias voltage could enhance carrier detrapping by suppressing the capture of structure defects and thus improve the temporal response of CZT detectors.

The scale factor of a superconducting gravimeter (SG) is usually calibrated by using simultaneous and co-located gravity measurements with the FG5-type absolute gravimeter (AG). In this paper, another new kind of absolute gravimeter-cold atom gravimeter (CAG) is first reported to calibrate the SG. Five-day side-by-side gravity measurements have been carried out by using our CAG (NIM-AGRb-1) to calibrate the SG (iGrav-012) located at Changping Campus of the National Institute of Metrology (NIM) of China. A weighted least-squares method is applied to determine the scale factor and the result is given as (-928.01±0.73) nm·^-2·V^-1 with a precision of 0.79‰. We have demonstrated that a calibration precision of 1‰ level can be achieved after 3 days of parallel observations at spring tide. The obtained calibration results are then compared with the previous calibration by FG5X-249, which shows that the calibration precision obtained by using NIM-AGRb-1 was slightly higher than FG5X-249 with the same time interval. The factors affecting the calibration precision are analyzed in the calibrations by means of different AGs. Finally, several calibration experiments for SG iGrav-012 are discussed. The final scale factor is estimated as (-927.58±0.36) nm·^-2·V^-1 with an accuracy of 0.39‰. Our main results demonstrate that the CAGs can be used for high-precision calibrations of SGs.

We numerically investigate the ground-state properties of a trapped Bose-Einstein condensate with quadrupole-quadrupole interaction. We quantitatively characterize the deformations of the condensate induced by the quadrupolar interaction. We also map out the stability diagram of the condensates and explore the trap geometry dependence of the stability.

The magnetic structure of CsCo₂Se₂ was investigated using single-crystal neutron diffraction technique. An antiferromagnetic transition with the propagation vector (0,0,1) was observed at T_N=78 K. The Co magnetic moment 0.772(6) μ_B at 10 K pointing in the basal plane couples ferromagnetically in the plane, which stacks antiferromagnetically along the c direction. Tuning and suppressing the interplane antiferromagnetic interaction may be crucial to induce a superconducting state in the material.

Sodium-ion batteries have attracted significant recent attention currently considering the limited available lithium resource. However, the energy density of sodium-ion batteries is still insufficient compared to lithium-ion batteries, mainly because of the unavailability of high-energy cathode materials. In this work, a novel sodium-rich layered oxide material (Na₂MnO₃) is reported with a dynamical stability similar to that of the Li₂MnO₃ structure and a high capacity of 269.69 mA·h·g¹, based on first-principles calculations. Sodium ion de-intercalation and anionic reaction processes are systematically investigated, in association with sodium ions migration phenomenon and structure stability during cycling of Na_xMnO₃ (1 ≤ x ≤ 2). In addition, the charge compensation during the initial charging process is mainly contributed by oxygen, where the small differences of the energy barriers of the paths 2c→4h, 4h→2c, 4h→4h, 2c→2b, and 4h→2b indicate the reversible sodium ion occupancy in transitional metal and sodium layers. Moreover, the slow decrease of the elastic constants is a clear indication of the high cycle stability. These results provide a framework to exploit the potential of sodium-rich layered oxide, which may facilitate the development of high-performance electrode materials for sodium-ion batteries.

Although various and unique properties of bulk nanobubbles have drawn researchers' attention over the last few years, their formation and stabilization mechanism has remained unsolved. In this paper, we use ultrasonic methods to produce bulk nanobubbles in the pure water and give a comprehensive study on the bulk nanobubbles properties and generation. The ultrasonic wave gives rise to constant oscillation in water where positive and negative pressure appears alternately. With the induced cavitation and presence of dissolved air, the bulk nanobubbles formed. “Nanosight” (which is a special instrument that combines dynamic light scattering with nanoparticle tracking analysis) was used to analyze the track and concentration of nanobubbles. Our results show that in our experiment, sufficient bulk nanobubbles were generated and we have proven they are not contaminations. We also found nanobubbles in the ultrasonic water change in both size and concentration with ultrasonic time.

Using first-principles calculations based on density functional theory, we show that the ground state of zigzag-edged graphene nanoribbons (ZGNRs) can be transformed from antiferromagnetic (AFM) order to ferromagnetic (FM) order by changing the substitutional sites of N or B dopants. This AFM-FM transition induced by substitutional sites is found to be a consequence of the competition between the edge and bulk states. The energy sequence of the edge and bulk states near the Fermi level is reversed in the AFM and FM configurations. When the dopant is substituted near the edge of the ribbon, the extra charge from the dopant is energetically favorable to occupy the edge states in AFM configuration. When the dopant is substituted near the center, the extra charge is energetically favorable to occupy the bulk states in FM configuration. Proper substrate with weak interaction is necessary to maintain the magnetic properties of the doped ZGNRs. Our study can serve as a guide to synthesize graphene nanostructures with stable FM order for future applications to spintronic devices.

In order to obtain an in-depth insight into the mechanism of charge compensation and capacity fading in LiCoO₂, the evolution of electronic structure of LiCoO₂ at different cutoff voltages and after different cycles are studied by soft x-ray absorption spectroscopy in total electron (TEY) and fluorescence (TFY) detection modes, which provide surface and bulk information, respectively. The spectra of Co L_2,3-edge indicate that Co contributes to charge compensation below 4.4 V. Combining with the spectra of O K-edge, it manifests that only O contributes to electron compensation above 4.4 V with the formation of local O 2p holes both on the surface and in the bulk, where the surficial O evolves more remarkably. The evolution of the O 2p holes gives an explanation to the origin of O₂^- or even O₂. A comparison between the TEY and TFY of O K-edge spectra of LiCoO₂ cycled in a range from 3 V to 4.6 V indicates both the structural change in the bulk and aggregation of lithium salts on the electrode surface are responsible for the capacity fading. However, the latter is found to play a more important role after many cycles.

Over the past 50 years, lunar laser ranging has made great contributions to the understanding of the Earth-Moon system and the tests of general relativity. However, because of the lunar libration, the Apollo and Lunokhod corner-cube retroreflector (CCR) arrays placed on the Moon currently limit the ranging precision to a few centimeters for a single photon received. Therefore, it is necessary to deploy a new retroreflector with a single and large aperture to improve the ranging precision by at least one order of magnitude. Here we present a hollow retroreflector with a 170-mm aperture fabricated using hydroxide-catalysis bonding technology. The precisions of the two dihedral angles are achieved by the mirror processing with a sub-arc-second precision perpendicularity, and the remaining one is adjusted utilizing an auxiliary optical configuration including two autocollimators. The achieved precisions of the three dihedral angles are 0.10 arc-second, 0.30 arc-second, and 0.24 arc-second, indicating the 68.5% return signal intensity of ideal Apollo 11/14 based on the far field diffraction pattern simulation. We anticipate that this hollow CCR can be applied in the new generation of lunar laser ranging.

We study how the decoherence of macroscopic objects originates intrinsically from the relativistic effect. With the degree of freedom of the center of mass (CM) characterizing the collective quantum state of a macroscopic object (MO), it is found that an MO consisting of N particles can decohere with a time scale of no more than √N^-1. Here, the special relativity can induce the coupling of the collective motion mode and the relative motion modes in an order of 1/c², which intrinsically results in the above minimum decoherence.