High Curie temperature ferromagnetic monolayer T-CrSH and valley physics of T-CrSH/WS2 heterostructure.

Two-dimensional magnetic materials are attracting widespread attention not only for their excellent applications in spintronic devices but also for their potential to regulate valley splitting, which is crucial for valleytronics. Herein, we design a monolayer Janus ferromagnetic semiconductor T-CrSH by using first-principles calculations. We reveal that monolayer T-CrSH has a magnetic moment of 3µB per unit cell, which is primarily contributed by the 3d orbitals of the Cr atom. Monte Carlo simulations suggest that the Curie temperature of T-CrSH is 193 K, and it can rise to 402 K when a 5% tensile strain is applied. Furthermore, the valley degeneracy of WS2 can be lifted when monolayer T-CrSH is used as a substrate. The obtained valley splitting in the conduction band is 13.7 meV and that in the valence band is 157.5 meV. In addition, the large valley polarization of 12.8 meV in the conduction band makes it easy to achieve an electron-doped valley Hall current and spin Hall current when performing in an in-plane electric field.

First-principles study of O2 and H2O adsorption on the Mg3Sb2(10-11) surface.

The degeneration of its thermoelectric properties in air is one of the factors that limit the practical application of high-performance n-type Mg3Sb2. In this work, first-principles calculations are conducted to study the adsorption of O2 and H2O on the Mg3Sb2(10-11) surface, as well as the effect of two strategies based on a terminating atom and Al doping on the adsorption performance. The calculated results show that the adsorbates prefer to adsorb on the bridge site of the surface because of the interaction with the outermost Mg atom. Sb termination can weaken the adsorption actions, due to the decreased interaction between the adsorbates and Mg atoms resulting from the decreased O-Mg bond strength. In addition, Al doping makes O2 prefer to interact with an Al atom rather than a Mg atom, which is beneficial for reducing Mg loss and thus improving the performance stability. This work aims to provide insight into improving the thermoelectric performance stability of Mg3Sb2-based materials.

Improving the Capacity of Quantum Dense Coding and the Fidelity of Quantum Teleportation by Weak Measurement and Measurement Reversal.

A protective scheme of quantum dense coding and quantum teleportation of the X-type initial state is proposed in amplitude damping noisy channel with memory using weak measurement and measurement reversal. Compared with the noisy channel without memory, the memory factor improves both the capacity of quantum dense coding and the fidelity of the quantum teleportation to a certain extent for the given damping coefficient. Although the memory factor can inhibit decoherence in some degree, it cannot eliminate it completely. In order to further overcome the influence of the damping coefficient, the weak measurement protective scheme is proposed, which found that the capacity and the fidelity can be efficiently improved by adjusting weak measurement parameter. Another practical conclusion is that, among the three initial states, the weak measurement protective scheme has the best protective effect on the Bell-state in terms of the capacity and the fidelity. For the channel with no memory and full memory, the channel capacity of quantum dense coding reaches two and the fidelity of quantum teleportation reaches one for the bit system; the Bell system can recover the initial state completely with a certain probability. It can be seen that the entanglement of the system can be well protected by the weak measurement scheme, which provides a good support for the realization of quantum communication.

Experimental Demonstration of Quantum Overlapping Tomography.

Quantum tomography is one of the major challenges of large-scale quantum information research due to the exponential time complexity. In this Letter, we develop and apply a Bayesian state estimation method to experimentally demonstrate quantum overlapping tomography [Phys. Rev. Lett. 124, 100401 (2020)PRLTAO0031-900710.1103/PhysRevLett.124.100401], a scheme intent on characterizing critical information of a many-body quantum system in logarithmic time complexity. By comparing the measurement results of full-state tomography and overlapping tomography, we show that overlapping tomography gives accurate information of the system with much fewer state measurements than full-state tomography.

Understanding the influence of Bi/Sb substitution on carrier concentration in Mg3Sb2-based materials: decreasing bandgap enhances the degree of impurity ionization.

Experimental results show an intriguing phenomenon that although Bi and Sb have the same number of valence electrons, Bi/Sb substitution increases the electron concentration of n-type Mg3Sb2-based materials. Using a combination of theoretical calculations and experimental synthesis, this work reveals the physical mechanism of the effect of Bi doping on carrier concentration. The increase in electron concentration mainly originates from the enhanced degree of ionization of donor impurity because of the decrease of conductivity effective mass and increase of dielectric constant caused by the narrowing of bandgap with Bi doping. Based on the collaborative optimization of the electrical and thermal transports, n-type Mg3.175Mn0.025Sb1.48Bi0.48Te0.04 exhibits the best thermoelectric performance with a peak zT of 1.85 at 725 K and an average zT of 1.21. This work demonstrates an effective strategy of bandgap engineering for the optimization of carrier concentration and provides insightful guidance for designing other thermoelectric materials.

Preparation and Analysis of Two-Dimensional Four-Qubit Entangled States with Photon Polarization and Spatial Path.

Entanglement states serve as the central resource for a number of important applications in quantum information science, including quantum key distribution, quantum precision measurement, and quantum computing. In pursuit of more promising applications, efforts have been made to generate entangled states with more qubits. However, the efficient creation of a high-fidelity multiparticle entanglement remains an outstanding challenge due to the difficulty that increases exponentially with the number of particles. We design an interferometer that is capable of coupling the polarization and spatial paths of photons and prepare 2-D four-qubit GHZ entanglement states. Using quantum state tomography, entanglement witness, and the violation of Ardehali inequality against local realism, the properties of the prepared 2-D four-qubit entangled state are analyzed. The experimental results show that the prepared four-photon system is an entangled state with high fidelity.

Experimental Investigation of the Robustness of a New Bell-Type Inequality of Triphoton GHZ States in Open Systems.

Knowing the level of entanglement robustness against quantum bit loss or decoherence mechanisms is an important issue for any application of quantum information. Fidelity of states can be used to judge whether there is entanglement in multi-particle systems. It is well known that quantum channel security in QKD can be estimated by measuring the robustness of Bell-type inequality against noise. We experimentally investigate a new Bell-type inequality (NBTI) in the three-photon Greenberger-Horne-Zeilinger (GHZ) states with different levels of spin-flip noise. The results show that the fidelity and the degree of violation of the NBTI decrease monotonically with the increase of noise intensity. They also provide a method to judge whether there is entanglement in three-particle mixed states.

Large improvement in thermoelectric performance of pressure-tuned Mg3Sb2.

The Mg3Sb2-based Zintl compound is a promising candidate for a high-performance thermoelectric material with the advantage of the component elements being low cost, non-toxic and earth-abundant. Here, we investigate the influence of pressure on the electronic structure and p-type and n-type thermoelectric transport properties of Mg3Sb2 by using density functional theory and Boltzmann transport theory. The energy gaps first increase and then decrease with the increasing of pressure, and a peak value of the valley degeneracy of conduction band occurs at 4 GPa. Based on the calculated band structures, the zT (figure of merit) values of p-type Mg3Sb2 under pressure are significantly enhanced, which predominantly originates from the boosted PF (power factor) contributed by the increased carrier's relaxation time. When the carrier concentration reaches 1 × 1020 cm-3, the PF of p-type Mg3Sb2 at 4 GPa is increased by 35% relative to that of the compound at 0 GPa, thus leading to a considerably improved zT of ∼0.62 at 725 K. Under the same conditions, due to the increased density of states effective mass, the n-type Mg3Sb2 exhibits a highest PF of ∼19 µW cm-1 K-2 and a peak zT of 1.7. Therefore, pressure tuning is an effective method to improve the p-type and n-type thermoelectric transport performance of Mg3Sb2-based Zintl compounds. This work on Mg3Sb2 under pressure may provide a new mechanism for the experimenters towards the enhancement of the thermoelectric performance of materials.

Experimentally Demonstrate the Spin-1 Information Entropic Inequality Based on Simulated Photonic Qutrit States.

Quantum correlations of higher-dimensional systems are an important content of quantum information theory and quantum information application. The quantification of quantum correlation of high-dimensional quantum systems is crucial, but difficult. In this paper, using the second-order nonlinear optical effect and multiphoton interference enhancement effect, we experimentally implement the photonic qutrit states and demonstrate the spin-1 information entropic inequality for the first time to quantitative quantum correlation. Our work shows that information entropy is an important way to quantify quantum correlation and quantum information processing.

HPHT Synthesis: Effects of the Synergy of Pressure Regulation and Atom Filling on the Microstructure and Thermoelectric Properties of Yb x Ba8-x Ga16Ge30.

Type-I clathrate compounds Yb x Ba8-x Ga16Ge30 have been synthesized by the high-pressure and high-temperature (HPHT) method rapidly. The effects of the synergy of atom filling and pressure regulation on the microstructure and thermal and electrical properties have been investigated. With the content of Yb atom increasing, the carrier concentration is improved, the electrical resistivity and the absolute Seebeck coefficient are decreased, while the thermal conductivity is reduced significantly. A series of extremely low lattice thermal conductivities are achieved, attributed to the enhancement of multiscale phonon scattering for the "rattling" of the filled guest atoms, the heterogeneous distribution of nano- and microstructures, grain boundaries, abundant lattice distortions, lattice deformations, and dislocations. As a result, a maximum ZT of about 1.07 at 873 K has achieved for the Yb0.5Ba7.5Ga16Ge30 sample.

Surface/Interface Engineering for Constructing Advanced Nanostructured Light-Emitting Diodes with Improved Performance: A Brief Review.

With the rise of nanoscience and nanotechnologies, especially the continuous deepening of research on low-dimensional materials and structures, various kinds of light-emitting devices based on nanometer-structured materials are gradually becoming the natural candidates for the next generation of advanced optoelectronic devices with improved performance through engineering their interface/surface properties. As dimensions of light-emitting devices are scaled down to the nanoscale, the plentitude of their surface/interface properties is one of the key factors for their dominating device performance. In this paper, firstly, the generation, classification, and influence of surface/interface states on nanometer optical devices will be given theoretically. Secondly, the relationship between the surface/interface properties and light-emitting diode device performance will be investigated, and the related physical mechanisms will be revealed by introducing classic examples. Especially, how to improve the performance of light-emitting diodes by using factors such as the surface/interface purification, quantum dots (QDs)-emitting layer, surface ligands, optimization of device architecture, and so on will be summarized. Finally, we explore the main influencing actors of research breakthroughs related to the surface/interface properties on the current and future applications for nanostructured light-emitting devices.

A Review of Perovskite Photovoltaic Materials' Synthesis and Applications via Chemical Vapor Deposition Method.

Perovskite photovoltaic materials (PPMs) have emerged as one of superstar object for applications in photovoltaics due to their excellent properties-such as band-gap tunability, high carrier mobility, high optical gain, astrong nonlinear response-as well as simplicity of their integration with other types of optical and electronic structures. Meanwhile, PPMS and their constructed devices still present many challenges, such as stability, repeatability, and large area fabrication methods and so on. The key issue is: how can PPMs be prepared using an effective way which most of the readers care about. Chemical vapor deposition (CVD) technology with high efficiency, controllability, and repeatability has been regarded as a cost-effective road for fabricating high quality perovskites. This paper provides an overview of the recent progress in the synthesis and application of various PPMs via the CVD method. We mainly summarize the influence of different CVD technologies and important experimental parameters (temperature, pressure, growth environment, etc.) on the stabilization, structural design, and performance optimization of PPMS and devices. Furthermore, current challenges in the synthesis and application of PPMS using the CVD method are highlighted with suggested areas for future research.

Experimental investigation of the information entropic Bell inequality.

Inequalities of information entropic play a fundamental role in information theory and have been employed effectively in finding bounds on optimal rates of various information-processing tasks. In this paper, we perform the first experimental demonstration of the information-theoretic spin-1/2 inequality using the high-fidelity entangled state. Furthermore, we study the evolution of information difference of entropy when photons passing through different noisy channels and give the experimental rules of the information difference degradation. Our work provides an new essential tool for quantum information processing and measurement, and offers new insights into the dynamics of quantum correlation in open systems.

Photoluminescence studies of SiC/SiO2 aloetic-shaped nanowires.

Room- and variable-temperature photoluminescence from 3C-SiC aloetic-shaped nanowires was presented. The SiC nanowires were prepared on Si(100) substrates by the reaction of methane with silicon dioxide. Scanning electron microscope (SEM) and X-ray diffraction (XRD) are used to characterization the nanowires. A green photoluminescence (PL) band centered at 2.34 eV is observed in the nanowires at room temperature. The results from variable-temperature photoluminescence show anomalous temperature dependencies of the spectral characteristics. The emission intensity increases with decreasing temperature until reaching an intensity maximum at about 155 K, then it decreases at lower temperatures. The emission energy has little shift following temperature variations. The anomalous temperature dependencies of PL results may be explained by quantum confinement effect and phonon participation in the emission process.

Extreme violation of local realism with a hyper-entangled four-photon-eight-qubit Greenberger-Horne-Zelinger state.

The highest qubit Ardehali inequality violation with 203 standard deviations is first experimentally demonstrated using the hyper-entangled four-photon-eight-qubit Greenberger-Horne-Zeilinger (GHZ) state. Moreover, we experimentally investigate the robustness of the Ardehali inequality for the four-, six-, and eight-qubit GHZ states in a rotary noisy environment systematically. Our results first validate the Ardehali' theoretical statement of relation between violation of Ardehali inequality and particle number, and proved that Ardehali inequality is more robust against noise in larger number qubit GHZ states, and provided an experimental benchmark for us to estimate the safety of quantum channel in the noisy environment.

Aloetic-shaped SiC nanowires: synthesis and field electron emission properties.

Novel ordered aloetic-shaped SiC nanowires were synthesized on a Si (100) substrate by reacting methane with silicon dioxide using iron as a catalyst. Their structure and chemical composition were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The wires have a tapered aloetic structure with a top diameter about 50-80 nm and a length about 10 microm. The field emission properties of the aloetic nanowires were investigated. A stable emission with current density of 0.525 mA/cm2 at an applied electric field of 2.2 V/microm and a low turn-on electric fields of 1.4 V/microm were observed. The excellent field emission properties indicate that the aloetic-shaped SiC nanowires may have potential applications in flat panel displays and electron field-emitting devices.