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Layered magnetic materials, such as MnBi2Te4, have drawn much attention owing to their potential for realizing 2D magnetism and possible topological states. Recently, FeBi2Te4, which is isostructural to MnBi2Te4, has been synthesized in experiment, but its detailed magnetic ordering and band topology have not been clearly understood yet. Here, based on first-principles calculations, we investigate the magnetic and electronic properties of FeBi2Te4 in bulk and 2D forms. We show that different from MnBi2Te4, the magnetic ground states of bulk, single-layer, and bilayer FeBi2Te4 all favor a 120∘ noncollinear antiferromagnetic ordering, and they are topologically trivial narrow-gap semiconductors. For the bilayer case, we find that a quantum anomalous Hall effect with a unit Chern number is realized in the ferromagnetic state, which may be achieved in experiment by an external magnetic field or by magnetic proximity coupling. Our work clarifies the physical properties of the new material system of FeBi2Te4 and reveals it as a potential platform for studying magnetic frustration down to 2D limit as well as quantum anomalous Hall effect.

The 5G IoT is very complicated and there are many factors that affect the network performance. Presently, the optimization of network is still the focus of research. Although the existing literature has done a large number of researches in this aspect, there have always been problems, such as complex algorithms. Based on the previous research, we propose a big data mining analysis method, which improves the comprehensive performance of the network by analyzing the relationship of massive data variables so as to optimize the combination of the network. In this paper, according to each of terminal variables at any moment such as power consumption, bandwidth, noise power, subcarrier bandwidth, interference power and coding efficiency, etc. we develop the mathematical modeling of principal component multiple regression. Then we simulate this scheme by edge computing technology and combine it with intelligent algorithms. The research results show that this method can effectively predict the data concerned, and the residual is the smallest. Therefore, the research provides an important basic for application of the approach to the mobile edge network optimization of IoTs.

Crystalline symmetry is a defining factor of the electronic band topology in solids, where many-body interactions often induce a spontaneous breaking of symmetry. Superconductors lacking an inversion center are among the best systems to study such effects or even to achieve topological superconductivity. Here, we demonstrate that

We predict a new family of two-dimensional (2D) rare earth monochalcogenide materials MX (M = Sc, Y; X = S, Se, Te). Based on first-principles calculations, we confirm their stability and systematically investigate their mechanical properties. We find that these materials are metallic and interestingly, they possess nodal lines in the low-energy band structure surrounding the whole Brillouin zone, protected by nonsymmorphic crystal symmetries in the absence of spin-orbit coupling (SOC). SOC opens small energy gaps at the nodal line, except for two high-symmetry points, at which fourfold degenerate 2D spin-orbit Dirac points are obtained. We show that these topological band features are robust under uniaxial and biaxial strains, but can be lifted by the shear strain. We also investigate the optical conductivities of these materials, and show that the transformation of the band structure under strain can be inferred from the optical absorption spectrum. Our work reveals a new family of 2D topological metal materials with interesting mechanical and electronic properties, which will facilitate the study of nonsymmorphic symmetry enabled nodal features in 2D., Comment: 15 pages, 4 figures

The network switching is one of the most important techniques, which keeps continuous communication between two users. A variety of approaches and strategies (such as fuzzy logic control, neural network, smart algorithm etc.) have been proposed to confront this problem. These approaches and strategies play an important role in reducing delays, decreasing drop call rates, and improving QoS during switching. However, the existing techniques and strategies often apply to some special scenarios, such as between WLAN and WiFi (or WiMAX, or 3G, or UTMS and LTE). Facing the ultra-dense heterogeneous network in the 5G communication system, this brings great difficulties to the switching, especially how to properly select a service network. Whether the existing methods and strategies are feasible remains to be studied. For solving the switching in a complication networks environment, a novel switching way is proposed in this paper. We adopt the technology of regional awareness and combine with Bayes’ decision strategy to explore the switching of ultra-dense heterogeneous network. This way effectively solves the difficult problem of selecting a service network in the convention. Finally, we analyze the err probability of the proposed way. The experimental results show that our scheme can properly select the switched network in the 5G system, and the probability of the handover error is the lowest, which ensures the rationality and effectiveness of the network handover. Therefore, the proposed way in this paper is feasible.

Response properties that are purely intrinsic to physical systems are of paramount importance in physics research, as they probe fundamental properties of band structures and allow quantitative calculation and comparison with experiment. For anomalous Hall transport in magnets, an intrinsic effect can appear at the second order to the applied electric field. We show that this intrinsic second-order anomalous Hall effect is associated with an intrinsic band geometric property -- the dipole moment of Berry-connection polarizability (BCP) in momentum space. The effect has scaling relation and symmetry constraints that are distinct from the previously studied extrinsic contributions. Particularly, in antiferromagnets with $\mathcal{PT}$ symmetry, the intrinsic effect dominates. Combined with first-principles calculations, we demonstrate the first quantitative evaluation of the effect in the antiferromagnet Mn$_{2}$Au. We show that the BCP dipole and the resulting intrinsic second-order conductivity are pronounced around band near degeneracies. Importantly, the intrinsic response exhibits sensitive dependence on the N\'{e}el vector orientation with a $2\pi$ periodicity, which offers a new route for electric detection of the magnetic order in $\mathcal{PT}$-invariant antiferromagnets., Comment: 5 pages, 3 figures

One big achievement in modern condensed matter physics is the recognition of the importance of various band geometric quantities in physical effects. As prominent examples, Berry curvature and the Berry curvature dipole are connected to the linear and the second-order Hall effects, respectively. Here, we show that the Berry connection polarizability (BCP) tensor, as another intrinsic band geometric quantity, plays a key role in the third-order Hall effect. Based on the extended semiclassical formalism, we develop a theory for the third-order charge transport and derive explicit formulas for the third-order conductivity. Our theory is applied to the two-dimensional (2D) Dirac model to investigate the essential features of the BCP and the third-order Hall response. We further demonstrate the combination of our theory with the first-principles calculations to study a concrete material system, the monolayer FeSe. Our work establishes a foundation for the study of third-order transport effects, and reveals the third-order Hall effect as a tool for characterizing a large class of materials and for probing the BCP in band structure., 7 pages, 4 figures

We report a comprehensive study of the centrosymmetric ${\mathrm{Re}}_{3}\mathrm{B}$ and noncentrosymmetric ${\mathrm{Re}}_{7}{\mathrm{B}}_{3}$ superconductors. At a macroscopic level, their bulk superconductivity (SC), with ${T}_{c}=5.1\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ (${\mathrm{Re}}_{3}\mathrm{B}$) and 3.3 K (${\mathrm{Re}}_{7}{\mathrm{B}}_{3}$), was characterized via electrical-resistivity, magnetization, and heat-capacity measurements, while their microscopic superconducting properties were investigated by means of muon-spin rotation and relaxation ($\ensuremath{\mu}\mathrm{SR}$). In both ${\mathrm{Re}}_{3}\mathrm{B}$ and ${\mathrm{Re}}_{7}{\mathrm{B}}_{3}$ the low-$T$ zero-field electronic specific heat and the superfluid density (determined via transverse-field $\ensuremath{\mu}\mathrm{SR}$) suggest a nodeless SC. Both compounds exhibit some features of multigap SC, as evidenced by the temperature-dependent upper critical fields ${H}_{\mathrm{c}2}(T)$, as well as by electronic band-structure calculations. The absence of spontaneous magnetic fields below the onset of SC, as determined from zero-field $\ensuremath{\mu}\mathrm{SR}$ measurements, indicates a preserved time-reversal symmetry in the superconducting state of both ${\mathrm{Re}}_{3}\mathrm{B}$ and ${\mathrm{Re}}_{7}{\mathrm{B}}_{3}$. Our results suggest that a lack of inversion symmetry and the accompanying antisymmetric spin-orbit coupling effects are not essential for the occurrence of multigap SC in these rhenium-boron compounds.

This paper aims at presenting a comparative analysis of different metaheuristic algorithms in the application of energy management for fuel cell-based hybrid emergency power unit within electrical aircraft. Two energy management conventional strategies are employed while optimizing the operating temperature. Both the external energy maximization and the equivalent consumption minimization strategies are dealt with. The most efficient up-to-date metaheuristic techniques such as the artificial bee colony, the grey wolf optimization, the cuckoo search, the mine blast algorithm, the whale optimization algorithm, the moth swarm algorithm, the harmony search, the modified flower pollination algorithm and the electromagnetic field optimization are considered. The overall index of optimization performance is considered as a function of hydrogen consumption, overall system efficiency, variations of states of charge and stresses in different energy sources. The numerical simulations, through Matlab™/Simulink, highlights the capability of the different metaheuristic optimization techniques towards reducing the amount of consumed hydrogen in fuel cell-based emergency power unit in electrical aircrafts. The electromagnetic field optimization method results in significant hydrogen consumption reduction in comparison with the other proposed techniques.

The interplay between structural phase and electronic correlations has been an intriguing topic of research. An prominent example is the pressure-induced uncollapsed to collapsed tetragonal phase transition observed in CaFe$_2$As$_2$, which is accompanied with the emergence of superconductivity in the collapsed phase. Recently, a very similar structural phase transition was discovered in LaFe$_2$As$_2$, but in contrast to CaFe$_2$As$_2$, superconductivity was only observed in the uncollapsed phase, not the collapsed phase. Previous studies have attributed this puzzling observation to the differences in the two materials' band coherence, orbital occupation, and Fermi surface topology. Here, we present a comparative study of LaFe$_2$As$_2$ and CaFe$_2$As$_2$ using the DFT+DMFT method. Surprisingly, we find that although La appears to have a valence higher than Ca, the doped one electron actually primarily resides on the La site. This leads to almost the same total Fe-$3d$ occupancy and electronic correlation strength as well as similar Lifshiftz transition in the Fermi surface topology for the two materials. In addition, we show that the two materials in both structural phases belong to the category of Hund's metals. Our results indicate that the electronic structures of LaFe$_2$As$_2$ and CaFe$_2$As$_2$ are not too different, which further suggest that superconductivity might also be induced in the collapsed phase of LaFe$_2$As$_2$ under similar non-hydrostatic conditions as for CaFe$_2$As$_2$., Comment: 6 pages, 4 figures

Nonlinear responses in transport measurements are linked to material properties not accessible at linear order1 because they follow distinct symmetry requirements2-5. While the linear Hall effect indicates time-reversal symmetry breaking, the second-order nonlinear Hall effect typically requires broken inversion symmetry1. Recent experiments on ultrathin WTe2 demonstrated this connection between crystal structure and nonlinear response6,7. The observed second-order nonlinear Hall effect can probe the Berry curvature dipole, a band geometric property, in non-magnetic materials, just like the anomalous Hall effect probes the Berry curvature in magnetic materials8,9. Theory predicts that another intrinsic band geometric property, the Berry-connection polarizability tensor10, gives rise to higher-order signals, but it has not been probed experimentally. Here, we report a third-order nonlinear Hall effect in thick Td-MoTe2 samples. The third-order signal is found to be the dominant response over both the linear- and second-order ones. Angle-resolved measurements reveal that this feature results from crystal symmetry constraints. Temperature-dependent measurement shows that the third-order Hall response agrees with the Berry-connection polarizability contribution evaluated by first-principles calculations. The third-order nonlinear Hall effect provides a valuable probe for intriguing material properties that are not accessible at lower orders and may be employed for high-order-response electronic devices. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version We acknowledge financial support from the Singapore National Research Foundation through its Competitive Research Program (CRP award numbers NRF-CRP21-2018-0007, NRF-CRP22-2019-0004 and NRF-CRP23-2019-0002), the Singapore Ministry of Education (grant number MOE2016-T3-1-006 (S)) and the A*Star QTE programme.

Topological phonons in crystalline materials have been attracting great interest. However, most cases studied so far are direct generalizations of the topological states from electronic systems. Here, we reveal a novel class of topological phonons -- the symmetry-enforced nodal-chain phonons, which manifest features unique for phononic systems. We show that with $D_{2d}$ little co-group at a non-time-reversal-invariant-momentum point, the phononic nodal chain is guaranteed to exist owing to the vector basis symmetry of phonons, which is a unique character distinct from electronic and other systems. Combined with the spinless character, this makes the proposed nodal-chain phonons enforced by symmorphic crystal symmetries. We further screen all 230 space groups, and find five candidate groups. Interestingly, the nodal chains in these five groups exhibit two different patterns: for tetragonal systems, they are one-dimensional along the fourfold axis; for cubic systems, they form a three-dimensional network structure. Based on first-principles calculations, we identify K$_{2}$O as a realistic material hosting almost ideal nodal-chain phonons. We show that the effect of LO-TO splitting, another unique feature for phonons, helps to expose the nodal-chain phonons in K$_{2}$O in a large energy window. In addition, all the five candidate groups have spacetime inversion symmetry, so the nodal chains also feature a quantized $\pi$ Berry phase. This leads to drumhead surface phonon modes that must exist on multiple surfaces of a sample., Comment: 6 pages, 4 figures

Recently, intensive studies have revealed fascinating physics, such as charge density wave and superconducting states, in the newly synthesized kagome-lattice materials $A$V$_3$Sb$_5$ ($A$=K, Rb, Cs). Despite the rapid progress, fundamental aspects like the magnetic properties and electronic correlations in these materials have not been clearly understood yet. Here, based on the density functional theory plus the single-site dynamical mean-field theory calculations, we investigate the correlated electronic structure and the magnetic properties of the KV$_3$Sb$_5$ family materials in the normal state. We show that these materials are good metals with weak local correlations. The obtained Pauli-like paramagnetism and the absence of local moments are consistent with recent experiment. We reveal that the band crossings around the Fermi level form three groups of nodal lines protected by the spacetime inversion symmetry, each carrying a quantized $\pi$ Berry phase. Our result suggests that the local correlation strength in these materials appears to be too weak to generate unconventional superconductivity, and non-local electronic correlation might be crucial in this kagome system., Comment: 6 pages, 4 figures

Higher-order topological insulators have attracted great research interest recently. Different from conventional topological insulators, higher-order topological insulators do not necessarily require spin-orbit coupling, which makes it possible to realize them in spinless systems. Here, we study phonons in 2D graphyne family materials. By using first-principle calculations and topology/symmetry analysis, we find that phonons in both graphdiyne and $\gamma$-graphyne exhibit a second-order topology, which belongs to the specific case known as real Chern insulator. We identify the nontrivial phononic band gaps, which are characterized by nontrivial real Chern numbers enabled by the spacetime inversion symmetry. The protected phonon corner modes are verified by the calculation on a finite-size nanodisk. Our study extends the scope of higher-order topology to phonons in real materials. The spatially localized phonon modes could be useful for novel phononic applications., Comment: 6 pages, 5figures

Chiral superconductors are novel topological materials with finite angular momentum Cooper pairs circulating around a unique chiral axis, thereby spontaneously breaking time-reversal symmetry. They are rather scarce and usually feature triplet pairing: a canonical example is the chiral p-wave state realized in the A-phase of superfluid He3. Chiral triplet superconductors are, however, topologically fragile with the corresponding gapless boundary modes only weakly protected against symmetry-preserving perturbations in contrast to their singlet counterparts. Using muon spin relaxation measurements, here we report that the weakly correlated pnictide compound LaPt3P has the two key features of a chiral superconductor: spontaneous magnetic fields inside the superconducting state indicating broken time-reversal symmetry and low temperature linear behaviour in the superfluid density indicating line nodes in the order parameter. Using symmetry analysis, first principles band structure calculation and mean-field theory, we unambiguously establish that the superconducting ground state of LaPt3P is a chiral d-wave singlet., Nature Communications, 12 (1), ISSN:2041-1723

Anisotropy is a general feature in materials. Strong anisotropy could lead to interesting physical properties and useful applications. Here, based on first-principles calculations and theoretical analysis, we predict a stable two-dimensional (2D) material---the monolayer MoOCl$_2$, and show that it possesses intriguing properties related to its high anisotropy. Monolayer MoOCl$_2$ can be readily exfoliated from the van der Waals layered bulk, which has already been synthesized. We show that a high in-plane anisotropy manifests in the structural, phononic, mechanical, electronic, and optical properties of monolayer MoOCl$_2$. The material is a metal with highly anisotropic Fermi surfaces, giving rise to open orbits at the Fermi level, which can be probed in magneto-transport. Remarkably, the combination of high anisotropy and metallic character makes monolayer MoOCl$_2$ an almost ideal hyperbolic material. It has two very wide hyperbolic frequency windows from 0.41 eV (99 THz) to 2.90 eV (701 THz), and from 3.63 eV (878 THz) to 5.54 eV (1340 THz). The former window has a large overlap with the visible spectrum, and the dissipation for most part of this window is very small. The window can be further tuned by the applied strain, such that at a chosen frequency, a transition between elliptic and hyperbolic character can be induced by strain. Our work discovers a highly anisotropic 2D metal with extraordinary properties, which holds great potential for electronic and optical applications., Comment: 8 panges, 7 figures

Antimony selenide (${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$) consists of one-dimensional ribbons that are van der Waals bonded to each other. Due to its favorable optoelectronic properties, it is a promising material for solar energy conversion. Owing to its narrow direct band gap and its high absorption coefficient it is an efficient absorber for solar light. Besides, it is cheap, stable in harsh environments, and abundant with low toxicity. For its use in solar devices, efficient transport of photoexcited charge carriers towards the active interface and long lifetimes at sufficiently high energies are mandatory. Here time-resolved two-photon photoemission experiments on the (100) surface of ${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$ are presented. Data were taken along and perpendicular to the direction of the one-dimensional ribbons in order to unravel the anisotropic lifetimes and relaxation dynamics of photoexcited charge carriers. In both cases, various conduction bands could be populated and within the first picosecond ultrafast scattering towards the lowest conduction band was observed. Moreover, long lifetimes of up to 35 ps in the conduction band bottom at the surface were obtained and no sign of trapping in defect states was found. These measurements shed light on the relaxation and scattering of free carriers in ${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$, which is the key for the design of ${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$-based electrodes.

We report two reversible pressure-induced isosymmetric phase transitions in $\ensuremath{\alpha}\ensuremath{-}\mathrm{A}{\mathrm{g}}_{2}\mathrm{S}$ that are accompanied by two compressive anomalies at 7.5 and 16 GPa, respectively. The first transition arises from a sudden and drastic puckering of the wrinkled Ag-S layers, which leads to an anomalous structural softening at high pressure and gives rise to the ultrahigh compressive ductility in $\ensuremath{\alpha}\ensuremath{-}\mathrm{A}{\mathrm{g}}_{2}\mathrm{S}$. The second transition stems from a pressure-driven electronic state crossover from a conventional semiconductor to a topological metal. The band-crossing points near the Fermi energy form a nodal-line structure due to the preservation of the time-reversal and space-inversion symmetries under pressure. Our findings not only reveal the underlying mechanism responsible for the ultrahigh ductility in this class of inorganic semiconductors, but also provide a distinctive member to the growing family of topological metals and semimetals.

We report the discovery of Zr$_3$Ir as a new type of unconventional noncentrosymmetric superconductor (with $T_c = 2.3$ K), here investigated mostly via muon-spin rotation/relaxation ($\mu$SR) techniques. Its superconductivity was characterized using magnetic susceptibility, electrical resistivity, and heat capacity measurements. The low-temperature superfluid density, determined via transverse-field $\mu$SR and electronic specific heat, suggests a fully-gapped superconducting state. The spontaneous magnetic fields, revealed by zero-field $\mu$SR below $T_c$, indicate the breaking of time-reversal symmetry in Zr$_3$Ir and, hence, the unconventional nature of its superconductivity. By using symmetry arguments and electronic-structure calculations we obtain a superconducting order parameter that is fully compatible with the experimental observations. Hence, our results clearly suggest that Zr$_3$Ir represents a new member of noncentrosymmetric superconductors with broken time-reversal symmetry., Comment: 6 pages, 4 figuress; supplementary materials can be accessed from corresponding authors

Superconducting materials with a nontrivial band structure are potential candidates for topological superconductivity. Here, by combining muon-spin rotation and relaxation ($\mu$SR) methods with theoretical calculations, we investigate the superconducting and topological properties of the rock-salt-type compounds NbC and TaC (with$T_c$ = 11.5 and 10.3 K, respectively). At a macroscopic level, the magnetization and heat-capacity measurements under applied magnetic field provide an upper critical field of 1.93 and 0.65 T for NbC and TaC, respectively. The low-temperature superfluid density, determined by transverse-field $\mu$SR and electronic specific-heat data, suggest a fully-gapped superconducting state in both NbC and TaC, with a zero-temperature gap $\Delta_0 = 1.90$ and 1.45 meV, and a magnetic penetration depth $\lambda_0$ = 141 and 77 nm, respectively. Band-structure calculations suggest that the density of states at the Fermi level is dominated by the Nb $4d$- (or Ta $5d$-) orbitals, which are strongly hybridized with the C $p$-orbitals to produce large cylinder-like Fermi surfaces, similar to those of high-$T_c$ iron-based superconductors. Without considering the spin-orbit coupling (SOC) effect, the first Brillouin zone contains three closed node lines in the bulk band structure, protected by time-reversal and space-inversion symmetry. When considering SOC, its effects in the NbC case appear rather modest. Therefore, the node lines may be preserved in NbC, hence proposing it as a potential topological superconductor., Comment: 10 pages, 12 figures, accepted by Physical Review B

A characteristic of a Fermi liquid is the ${T}^{2}$ dependence of its resistivity, sometimes referred to as the Baber law. However, for most metals, this behavior is only restricted to very low temperatures, usually below 20 K. Here, we experimentally demonstrate that for the single-crystal van der Waals layered material $\mathrm{MoOC}{\mathrm{l}}_{2}$, the Baber law holds in a wide temperature range up to \ensuremath{\sim}120 K, indicating that the electron-electron scattering plays a dominant role in this material. Combining with the specific heat measurement, we find that the modified Kadowaki-Woods ratio of the material agrees well with many other strongly correlated metals. Furthermore, in the magnetotransport measurement, a colossal magnetoresistance is observed, which reaches \ensuremath{\sim}350% at 9 T and displays no sign of saturation. With the help of first-principles calculations, we attribute this behavior to the presence of open orbits on the Fermi surface. We also suggest that the dominance of electron-electron scattering is related to an incipient charge density wave state of the material. Our results establish $\mathrm{MoOC}{\mathrm{l}}_{2}$ as a strongly correlated metal and shed light on the underlying physical mechanism, which may open a new path for exploring the effects of electron-electron interaction in van der Waals layered structures.

The interplay between magnetism, band topology, and electronic correlation in low dimensions has been a fascinating subject of research. Here, we propose two-dimensional (2D) material systems which demonstrate such an interesting interplay. Based on first-principles calculations and structural search algorithms, we identify three lowest energy 2D CoSe structures, termed as the $\ensuremath{\alpha}$-, $\ensuremath{\beta}$-, and $\ensuremath{\gamma}$-CoSe. We show that $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-CoSe are two rare examples of 2D antiferromagnetic metals, which are related to their Fermi surfaces nesting features, and meanwhile, $\ensuremath{\gamma}$-CoSe is a ferromagnetic metal. They possess a range of interesting physical properties, including anisotropic valleys connected by crystalline symmetries, strain-tunable valley polarization, strain-induced metal-semiconductor and/or magnetic phase transitions, as well as topological band features such as the magnetic Weyl point and the magnetic Weyl loop. Remarkably, all the topological features here are robust against spin-orbit coupling. Some experimental aspects of our predictions have been discussed.

We propose an orbital magnetothermal effect wherein a temperature gradient generates an orbital magnetization (OM) for Bloch electrons, and we present a unified theory for electrically and thermally induced OM, valid for both metals and insulators. We reveal that there exists an intrinsic response of OM, for which the susceptibilities are completely determined by the band geometric quantities such as interband Berry connections, interband orbital moments, and the quantum metric. The theory can be readily combined with first-principles calculations to study real materials. As an example, we calculate the OM response in CrI$_{3}$ bilayers, where the intrinsic contribution dominates. The temperature scaling of intrinsic and extrinsic responses, the effect of phonon drag, and the phonon angular momentum contribution to OM are discussed., 4 pages, 1 tables, 2 figures

Interest in antimony selenide (Sb2Se3) has been constantly growing in the recent past, especially for its promising properties for applications in the field of solar energy technologies. Surprisingly, the surface properties of this material, which is built from van der Waals stacked one-dimensional (1D) ribbons, have not been studied in detail yet. Here we demonstrate that Sb2Se3 crystals cleave along the (100) planes. The resulting surface shows a pronounced 1D structure, reflecting the stacking of ribbons in the bulk crystal. The cleaving process leads to the formation of slightly tilted surface domains, with the tilt angles oriented invariably along the ribbon directions, suggesting a strong anisotropy of the internal friction forces. Our angle-resolved photoemission data reveal that the 1D character of the crystalline structure of this material is also reflected in its electronic band structure.

The operation of an unglazed, open-loop, solar-collector for residential pool heating was investigated experimentally under various flow conditions. The objective was to examine if solar pool collectors can be operated at lower flow conditions to minimize the pump energy while still providing sufficient thermal energy output to heat the pool. The system consists of a 20.5 m2 plastic tube, solar collector and a 36 m2 in-ground open-air pool. Key parameters were monitored over 38 days to validate a steady state model. The model achieved a good fit against the measured data and was used to simulate the system performance under various scenarios. Operating the system at low pump speed with a mass flow rate per unit collector area ( m ˙ / A C ) of 0.016 kgs−1m−2 was found to be optimal and achieved 60% pump energy savings. The coefficient of performance was increased by 2.5 times without compromising the thermal performance of the system in comparison to the Business as Usual (BAU) case. The optimal m ˙ / A C is approximately 50% of the lower limit specified by International and Australian Standards. Assuming all systems in Australia were operated under optimal conditions, annually 180 GWh of electricity consumption and 150 kilotonnes of CO2 emissions could be avoided.

Square-like tungsten oxide submicron materials were successfully synthesized via a simple hydrothermal route. It is found that the morphology, size and crystal structure of the products can be conveniently controlled by simply adjusting the reaction time and reaction temperature in the solution system. When used as the gas-sensing materials, the tungsten trioxide sensors show excellent responses to ammonia. Pt-loaded square-like WO3 can significantly improve the responses, and we also found that the Pt mass contents were configured to 1 wt% can realize the tallest response among the square-like WO3 and Pt-loaded WO3 for ammonia and other organic vapors. The experimental results indicate that a high sensing response of 100.09 is measured under 1000 ppm NH3/air gas at 270 °C. Furthermore, even at a low concentration of 1 ppm NH3/air, a good sensing response of 1.12 is acquired from this device. Moreover, responses with change in relative humidity from 10% to 90% were also investigated. Long-term stability test exhibits the gas sensor have good stability. The mechanism of enhanced sensor performance is also discussed. In addition, the gas sensor device demonstrated in this study has advantages including a relatively easy fabrication process, a simple structure, low cost, and a wide concentration detection range.

Based on first-principles calculations, we reported that external pressure can induce topological phase transition in alkaline-earth hexaborides, XB6 (X=Ca, Sr, Ba). It was revealed that XB6 is transformed from trivial semiconductors to topological node-line semimetals under moderate pressures when spin-orbit coupling (SOC) is ignored. The band inversion between B px (pz) and py orbitals at X point is responsible for the formation of node-line semimetals. Three node-line rings around X point are protected by the combination of the time-reversal and spatial inversion symmetries, and the drumhead surface bands are obtained in the interiors of the projected node-line rings. When SOC is included, tiny gaps (< 4.8 meV) open at the crossing lines, and the XB6 becomes strong topological insulators with Z2 indices (1;111). As the SOC-induced gap opening is negligible, our findings thus suggest ideal real systems for experimental exploration of the fundamental physics of topological node-line semimetals.