Multi-functional photonic spin Hall effect sensor controlled by phase transition

Photonic spin Hall effect(PSHE), as a novel physical effect in light–matter interaction, provides an effective metrological method for characterizing the tiny variation in refractive index(RI). In this work, we propose a multi-functional PSHE sensor based on VO_(2), a material that can reveal the phase transition behavior. By applying thermal control, the mutual transformation into different phase states of VO_(2) can be realized, which contributes to the flexible switching between multiple RI sensing tasks. When VO_(2) is insulating, the ultrasensitive detection of glucose concentrations in human blood is achieved. When VO_(2) is in a mixed phase, the structure can be designed to distinguish between the normal cells and cancer cells through no-label and real-time monitoring. When VO_(2) is metallic, the proposed PSHE sensor can act as an RI indicator for gas analytes. Compared with other multi-functional sensing devices with the complex structures, our design consists of only one analyte and two VO_(2) layers, which is very simple and elegant. Therefore, the proposed VO_(2)-based PSHE sensor has outstanding advantages such as small size, high sensitivity, no-label, and real-time detection, providing a new approach for investigating tunable multi-functional sensors.

Water Photomolecular Evaporation Due to Light-Mediated Ortho-Para Spin Transitions

Recent discoveries have revealed a groundbreaking phenomenon where light alone, without any thermal input, can induce water evaporation, termed the “photomolecular effect”. This study explores a novel hypothesis that this effect can be explained by ortho-para magnetic spin interactions in water molecules within the water-air interface layer. Water molecules, consisting of hydrogen and oxygen, exhibit different nuclear spin states: ortho-(triplet) and para-(singlet). The interaction of polarized light with these spin states may induce transitions between the rotational levels of ortho- and para-forms due to catalysts like triplet oxygen (O2) in its inhomogeneous magnetic field. Resonance pumping at 532 nm (~18,797 cm−1) due to the transition v1-v2-v3 ~ 0-8-2 (~18,796 cm−1) results in an increase in molecular energy sufficient to overcome intermolecular forces at the water surface, thereby causing evaporation. The proposed ortho-para conversion mechanism involves spin-orbit coupling and specific resonance conditions. This theory provides a quantum mechanical perspective on the photomolecular effect, potentially offering insights into natural processes such as cloud formation and climate modeling, as well as practical applications in solar desalination and industrial drying. Further experimental validation is required to confirm the role of spin interactions in light-induced water evaporation.

Topological phase transition in compressed van der Waals superlattice heterostructure BiTeCl/HfTe_(2)

Based on first-principles calculations,we investigate the electronic band structures and topological properties of heterostructure BiTeCl/HfTe_(2) under c-direction strain.In the primitive structure,this material undergoes a phase transition from an insulator with a narrow indirect gap to a metal by strong spin-orbital coupling.When strain effect is considered,band inversion at time-reversal invariant point Z is responsible for the topological phase transition.These nontrivial topologies are caused by two different types of band crossings.The observable topological surface states in(110)surface also support that this material experiences topological phase transition twice.The layered heterostructure with van der Waals force provides us with a new desirable platform upon which to control topological phase transition and construct topological superconductors.

Electronic structure and spin state regulation of vanadium nitride via a sulfur doping strategy toward flexible zinc-air batteries

Owing to the distinctive structural characteristics,vanadium nitride(VN)is highly regarded as a catalyst for oxygen reduction reaction(ORR)in zinc-air batteries(ZABs).However,VN exhibits limited intrinsic ORR activity due to the weak adsorption ability to O-containing species.Here,the S-doped VN anchored on N,S-doped multi-dimensional carbon(S-VN/Co/NS-MC)was constructed using the solvothermal and in-situ doping methods.Incorporating sulfur atoms into VN species alters the electron spin state of vanadium in the S-VN/Co/NS-MC for regulating the adsorption energy of vanadium sites to oxygen molecules.The introduced sulfur atoms polarize the V 3d_(z)^(2) electrons,shifting spin-down electrons closer to the Fermi level in the S-VN/Co/NS-MC.Consequently,the introduction of sulfur atoms into VN species enhances the adsorption energy of vanadium sites for oxygen molecules.The*OOH dissociation transitions from being unspontaneous on the VN surface to a spontaneous state on the S-doped VN surface.Then,the ORR barrier on the S-VN/Co/NS-MC surface is reduced.The S-VN/Co/NS-MC demonstrates a higher half-wave potential and limiting current density compared to the VN/Co/N-MC.The S-VN/Co/NS-MC-based liquid ZABs display a power density of 195.7 m W cm^(-2),a specific capacity of 815.7 m A h g^(-1),and a cycling stability exceeding 250 h.The S-VN/Co/NS-MC-based flexible ZABs are successfully employed to charge both a smart watch and a mobile phone.This approach holds promise for advancing the commercial utilization of VN-based catalysts in ZABs.

Neural network study of the nuclear ground-state spin distribution within a random interaction ensemble

The distribution of the nuclear ground-state spin in a two-body random ensemble(TBRE)was studied using a general classification neural network(NN)model with two-body interaction matrix elements as input features and the corresponding ground-state spins as labels or output predictions.The quantum many-body system problem exceeds the capability of our optimized NNs in terms of accurately predicting the ground-state spin of each sample within the TBRE.However,our NN model effectively captured the statistical properties of the ground-state spin because it learned the empirical regularity of the ground-state spin distribution in TBRE,as discovered by physicists.

Quantitative determination of the critical points of Mott metal–insulator transition in strongly correlated systems

Mottness is at the heart of the essential physics in a strongly correlated system as many novel quantum phenomena occur in the metallic phase near the Mott metal–insulator transition. We investigate the Mott transition in a Hubbard model by using the dynamical mean-field theory and introduce the local quantum state fidelity to depict the Mott metal–insulator transition. The local quantum state fidelity provides a convenient approach to determining the critical point of the Mott transition. Additionally, it presents a consistent description of the two distinct forms of the Mott transition points.

Pressure induced insulator to metal transition in quantum spin liquid candidate NaYbS_(2)

Pressure induced insulator to metal transition followed by the appearance of superconductivity has been observed recently in inorganic quantum spin liquid candidate NaYbSe_(2).In this paper,we study the properties of isostructural compound NaYbS_(2)under pressure.It is found that the resistance of Na YbS_(2)single crystal exhibits an insulating state below 82.9 GPa,but with a drop of more than six orders of magnitude at room temperature.Then a minimum of resistance is observed at about 100.1 GPa and it moves to lower temperature with further compression.Finally,a metallic state in the whole temperature range is observed at about 130.3 GPa accompanied by a non-Fermi liquid behavior below 100 K.The insulator to metal transition,non-monotonic resistance feature and non-Fermi liquid behavior of NaYbS_(2)under pressure are similar to those of NaYbSe_(2),suggesting that these phenomena might be the universal properties in NaLnCh_(2)(Ln=rare earth,Ch=O,S,Se)system.

Floquet dynamical quantum phase transitions in transverse XY spin chains under periodic kickings

Floquet dynamical quantum phase transitions(DQPTs),which are nonanalytic phenomena recuring periodically in time-periodic driven quantum many-body systems,have been widely studied in recent years.In this article,the Floquet DQPTs in transverse XY spin chains under the modulation ofδ-function periodic kickings are investigated.We analytically solve the system,and by considering the eigenstate as well as the ground state as the initial state of the Floquet dynamics,we study the corresponding multiple Floquet DQPTs emerged in the micromotion with different kicking moments.The rate function of return amplitude,the Pancharatnam geometric phase and the dynamical topological order parameter are calculated,which consistently verify the emergence of Floquet DQPTs in the system.

Effects of Spin Transition and Cation Substitution on the Optical Properties and Iron Partitioning in Carbonate Minerals

The high-pressure behavior of deep carbonate dictates the state and dynamics of oxidized carbon in the Earth's mantle,playing a vital role in the global carbon cycle and potentially influencing long-term climate change.Optical absorption and Raman spectroscopic measurements were carried out on two natural carbonate samples in diamond-anvil cells up to 60 GPa.Mg-substitution in high-spin siderite FeCO_(3)increases the crystal field absorption band position by approximately 1000 cm^(-1),but such an effect is marginal at>40 GPa when entering the low-spin state.The crystal field absorption band of dolomite cannot be recognized upon compression to 45.8 GPa at room temperature but,in contrast,the high-pressure polymorph of dolomite exhibits a strong absorption band at frequencies higher than(Mg,Fe)CO_(3)in the lowspin state by 2000–2500 cm^(-1).Additionally,these carbonate minerals show more complicated features for the absorption edge,decreasing with pressure and undergoing a dramatic change through the spin crossover.The optical and vibrational properties of carbonate minerals are highly correlated with iron content and spin transition,indicating that iron is preferentially partitioned into low-spin carbonates.These results shed new light on how carbonate minerals evolve in the mantle,which is crucial to decode the deep carbon cycle.

Rovibrational State-Selectivity in Photoassociation through Multi-photon Transitions

The rovibrational state-selectivity in photoassociation （PA） is investigated for the ground electronic state of OH radical. The calculated results show that population can be transferred from continuum state to the target states through three-, four-, and nine-photon transitions by choosing suitable pulse parameters and initial collision energy. To control population transfer to a lower rovibrational state, a shorter pulse frequency has to be chosen and the photon number transferred to target state should be increased. In PA process, some associated OH radicals can be dissociated via intermediate and background states, which decreases the nal population of the target state.

State Transition, Is It a Photochemical or Non-photochemical Processin Leaf in Response to Irradiance?

The response of steady-state fluorescence (Fs) to irradiance in apple (Malus pumila Mill. cv. Tengmu No.1/Malus hupehensis Rehd.) leaf increased and decreased at light levels below and above 400 mumol(.)m(-2.)s(-1) photosynthetic photon flux density (PPFD), respectively, while the light-adapted maximal fluorescence (Fm') and minimal fluorescence (Fo') decreased constantly with the increasing PPFD, and the closure of photosystem 11 reaction center (PS 11 RC) increased continuously, reflected by the chlorophyll fluorescence parameter of (Fs-Fo')/(Fm'-Fo'). These facts indicated that decrease of Fs above 400 mumol(.)m(-2.)s(-1) PPFD was not caused by closure of PS 11 RC, but was mainly resulted from the process of light transfer from light-harvesting complex II (LHC II) to PS II RC. In the presence of N- ethylmaleimide (NEM), an inhibitor of photosynthetic state transition, Fs kept on increasing in apple leaf at light levels from 400 to 700 mumol(.)m(-1.)s(-1), which was the photosynthetic saturation irradiance of apple leaves. In addition, Fs still increased at light levels over 700 mumol(.)m(-2.)s(-1) in apple leaf pre-treated with dithiothreitol (DTT), an inhibitor of xanthophyll cycle. These changes showed that state transition and xanthophyll cycle caused a decrease of Fs in apple leaf at light levels below and above the photosynthetic saturation irradiance, respectively. When apple leaf was pre-treated with NEM, the PS II apparent rate of photochemical reaction (P-rate) and photochemical quenching (qP) decreased significantly in the light range of 600-800 mumol(.)m(-2.)s(-1), but the non-photochemical quenching (qN) existed a small increase at 600-800 mumol(.)m(-2.)s(-1) and a decrease above 800 mumol(.)m(-2.)s(-1). These phenomena suggested that state transition was mainly a photochemical and a non-photochemical process in apple leaf responding to light lower and higher than photosynthetic saturation irradiance, respectively.

MoiréDirac fermions in transition metal dichalcogenides heterobilayers

Monolayer group-VIB transition metal dichalcogenides(TMDs)feature low-energy massive Dirac fermions,which have valley contrasting Berry curvature.This nontrivial local band topology gives rise to valley Hall transport and optical selection rules for interband transitions that open up new possibilities for valleytronics.However,the large bandgap in TMDs results in relatively small Berry curvature,leading to weak valley contrasting physics in practical experiments.Here,we show that Dirac fermions with tunable large Berry curvature can be engineered in moirésuperlattice of TMD heterobilayers.These moiréDirac fermions are created in a magnified honeycomb lattice with its sublattice degree of freedom formed by two local moirépotential minima.We show that applying an on-site potential can tune the moiréflat bands into helical ones.In short-period moirésuperlattice,we find that the two moirévalleys become asymmetric,which results in a net spin Hall current.More interestingly,a circularly polarized light drives these moiréDirac fermions into quantum anomalous Hall phase with chiral edge states.Our results open a new possibility to design the moiré-scale spin and valley physics using TMD moiréstructures.

Optimal Precursors Triggering the Kuroshio Extension State Transition Obtained by the Conditional Nonlinear Optimal Perturbation Approach

In this study, the initial perturbations that are the easiest to trigger the Kuroshio Extension （KE） transition connecting a basic weak jet state and a strong, fairly stable meandering state, are investigated using a reduced-gravity shallow water ocean model and the CNOP （Conditional Nonlinear Optimal Perturbation） approach. This kind of initial perturbation is called an optimal precursor （OPR）. The spatial structures and evolutionary processes of the OPRs are analyzed in detail. The results show that most of the OPRs are in the form of negative sea surface height （SSH） anomalies mainly located in a narrow band region south of the KE jet, in basic agreement with altimetric observations. These negative SSH anomalies reduce the merid- ional SSH gradient within the KE, thus weakening the strength of the jet. The KE jet then becomes more convoluted, with a high-frequency and large-amplitude variability corresponding to a high eddy kinetic energy level; this gradually strengthens the KE jet through an inverse energy cascade. Eventually, the KE reaches a high-energy state characterized by two well defined and fairly stable anticyclonic meanders. Moreover, sensitivity experiments indicate that the spatial structures of the OPRs are not sensitive to the model parameters and to the optimization times used in the analysis.

A circular zone counting method of identifying a Duffing oscillator state transition and determining the critical value in weak signal detection

Identifying state transition and determining the critical value of the Duffing oscillator are crucial to indicating external signal existence and have a great influence on detection accuracy in weak signal detection. A circular zone counting （CZC） method is proposed in this paper, by combining the Duffing oscillator＇s phase trajectory feature and numerical calculation for quickly and accurately identifying state transition and determining the critical value, to realize a high- efficiency weak signal detection. Detailed model analysis and method construction of the CZC method are introduced. Numerical experiments into the reliability of the proposed CZC method compared with the maximum Lyapunov exponent （MLE） method are carried out. The CZC method is demonstrated to have better detecting ability than the MLE method, and furthermore it is simpler and clearer in calculation to extend to engineering application.

Use of Solid State Carbothermic Reduction in Production of Transition Metals and Their Carbides

The use of solid state carbothermic reduction as a precursor to the smelting of transition metal ores was examined . The advantages of the introduction of a prereduction stage include enabling the more efficient use of fines and the achievement of higher energy efficiencies. A solid state reduction using carbon as the reductant offers a simpler alternative for their treatment. Subsequent treatment of the reduced material could include intensive bath smelting to produce ferroalloys or, in some case, solid state separation of the transition metal carbide where this has commercial significance.

Effect of content and spin state of iron on electronic properties and floatability of iron-bearing sphalerite:A DFT+U study

Iron is an impurity widely occurred in sphalerite,and its effect on sphalerite flotation is complex.In this work,the effects of iron content and spin state on electronic properties and floatability of iron-bearing sphalerite are comprehensively studied using density functional theory Hubbard U(DFT+U)calculations combined with coordination chemistry flotation.The band gap of ideal sphalerite is 3.723 eV,and thus electron transition is difficult to occur,resulting in poor floatability.The results suggest the band gap of sphalerite decreases with increasing iron content.For low iron content,the decreased band gap facilitates electron transition;at this case,Fe^(2+)in a high-spin state possesses oneπelectron pair,which can form a weakπ-backbonding with xanthate,causing increasing floatability.However,for medium and high iron-bearing sphalerite,with the further decrease of band gap,Fe^(2+)is oxidized to Fe^(3+)due to electrochemical interaction,and henceπ-backbonding is eliminated,leading to lower floatability of iron-bearing sphalerite,which is consistent with the flotation experimental results.This work could give a deeper understanding of how sphalerite flotation behaviors are affected by iron content.

Theoretical Study of Reaction Paths and Transition States on Conversion Methane into C_2 Hydrocarbons Through Plasma

The direct synthesis of C2 hydrocarbons （ethylene, acetylene and ethane） from methane is one of the most important task in C1 chemistry. Higher conversion of methane and selectivity to C2 hydrocarbons can be real-ized through plasma reaction. In order to explore the reaction process and mechanism, the possible reaction paths （1）—（4） were proposed on coupling reaction of methane through plasma and studied theoretically using semi-PM3 method [PM3 is parameterization method of modified neglect of diatomic overlap （MNDO）] including determining the transition state, calculating the activation energy and thermodynamic state functions and analyzing the bond or-der and intrinsic reaction coordinate. The reaction heat results indicate that the reactions （2） and （4） are exothermic, while reactions of （1） and （3） are endothermic. The activation energy results show that activation energy for reac-tions （1） and （2） was much lower than that of reaction paths （3） and （4）. Therefore, paths （1） and （2） is the favorable reaction path energetically. More interestingly by comparing the intrinsic reaction coordinated （IRC） of the reaction paths （1） and （2）, it is found that the variations of bond lengths in reaction path （1） has a crucial effect on the poten-tial energy, while in reaction path （2）, the adjustment of the system geometry also contributes to the whole potential energy of the system.

Transition state to mode locking in a passively mode-locked erbium-doped fibre ring laser

The transition state between the continuous wave region and the mode-locked region in a passively mode-locked erbium-doped fibre ring laser has been experimentally observed by utilizing the nonlinear polarization rotation technique. When the pump power reaches the mode-locked threshold, the metastable pulse train with a tunable repetition rate is obtained in the transition from the continuous wave state to the passive mode-locked state via proper adjustment of the polarization controller. A simpie model has been established to explain the experimental observation.

Effects of electron correlation and the Breit interaction on one- and two-electron one-photon transitions in double K hole states of He-like ions(10 ≤ Z ≤ 47)

The x-ray energies and transition rates associated with single and double electron radiative transitions from the double K hole state 2s2p to the 1s2s and 1s^2 configurations of 11 selected He-like ions(10 ≤ Z ≤ 47) are calculated using the fully relativistic multi-configuration Dirac–Fock method(MCDF). An appropriate electron correlation model is constructed with the aid of the active space method, which allows the electron correlation effects to be studied efficiently. The contributions of the electron correlation and the Breit interaction to the transition properties are analyzed in detail. It is found that the two-electron one-photon(TEOP) transition is correlation sensitive. The Breit interaction and electron correlation both contribute significantly to the radiative transition properties of the double K hole state of the He-like ions. Good agreement between the present calculation and previous work is achieved. The calculated data will be helpful to future investigations on double K hole decay processes of He-like ions.

Theoretical Study on the Transition State of N-nitropyrazoles Rearrangement Reaction

Theoretical studies on the rearrangement reactions of nitropyrazoles have beeninvestigated. In order to gain a better understanding of the intermediate process of rearrangementreactions, the transition states of the rearrangement reactions were obtained by TS method at theB3LYP/6-311G（d, p） level of theory. The natural bond orbital charge, electrostatic potential andfrontier molecular orbital of the molecules in the process of rearrangement were analyzed, and thesolvent effect was also discussed. The rearrangement of nitropyrazoles involves two transitionstates and one intermediate, and the nitro group and hydrogen atom are two transfer groups forrearrangement reactions. The migration of these two groups leads to the change of chargedistribution and molecular structure. The structural changes of the molecules in different solventsare not significant, but the dipole moment of the molecule has obvious change.