Phase Transition in Two-Dimensional Josephson-Junction Arrays

The self-charging model of two-dimensional Josephson-junction arrays at T = 0 is studied by the coupled cluster expansion method. The calculated results for the mass gap converge nicely. Besides the critical point, we also determine the critical parameters at T = 0. The system displays a second-order phase transition and the results are consistent with those obtained by other methods.     

Magnetic Phase Transition in Two-Dimensional CrBr3 Probed by a Quantum Sensor

Recently, magnetism in two-dimensional(2 D) van der Waals(vd W) materials has attracted wide interests. It is anticipated that these materials will stimulate discovery of new physical phenomena and novel applications. The capability to quantitatively measure the magnetism of 2 D magnetic vd W materials is essential to understand these materials. Here we report on quantitative measurements of ferromagnetic-to-paramagnetic phase transition of an atomically thin(down to 11 nm) vd W magnet, namely C...     

Self-Organization and Phase Transition in Two-Dimensional Traffic-Flow Model

An analytical investigation is made on two-dimensional traffic-flow model with alternative movement and exclude-volume effect between right and up arrows. Several exact results are obtained, including the upper critical density above which there are only jamming configurations, and the lower critical density below which there are only moving configurations. The observed jamming transition takes place at another critical density p_c(N), which is in the intermediate region between the lower and upper critical densities. This transition is suggested to be a second-order phase transition, the order parameter is found. The nature of self-organization, ergodicity breaking and synchronization are discussed. Comparison with the sandpile model is made.     

Magnetic Impurity Band and Photoinduced Magnetic Phase Transition in Diluted Magnetic Semiconductors

Applying the dynamical coherent potential approximation (dynamical CPA) to a model of diluted magnetic semiconductors (DMSs), in which both random impurity distribution and thermal fluctuation of localized spins are taken into account, the spin-polarized band and the carrier spin polarization are calculated for various magnetizations. In order to clarify the role of impurity depth on the occurrence of ferromagnetism, three typical cases are investigated: (a) II-VI DMS, (b) deep impurity level, and (c) strong exchange interaction. The present study reveals that the impurity depth of magnetic ions strongly enhances the carrier spin polarization (CSP) and accordingly, leads to a high Curie temperature. This means that photoinduced ferromagnetism with high Curie temperature can be expected in a DMS with a deep impurity depth and strong exchange interaction.     

Chiral Magnetic Effect and Chiral Phase Transition

We study the influence of the chiral phase transition on the chiral magnetic effect. The azimuthal charge-particle correlations as functions of the temperature are calculated. It is found that there is a pronounced cusp in the correlations as the temperature reaches its critical value for the QCD phase transition. It is predicted that there will be a drastic suppression of the charge-particle correlations as the collision energy in RHIC decreases to below a critical value. We show then the azimuthal charge-particle correlations can be the signal to identify the occurrence of the QCD phase transitions in RHIC energy scan experiments.     

Ballistic Transport through a Strained Region on Monolayer Phosphorene

We investigate quantum transport of carriers through a strained region on monolayer phosphorene theoretically.The electron tunneling is forbidden when the incident angle exceeds a critical value. The critical angles for electrons tunneling through a strain region for different strengths and directions of the strains are different.Owing to the anisotropic effective masses, the conductance shows a strong anisotropic behavior. By tuning the Fermi energy and strain, the channels can be transited from opaque to transparent, which provides us with an efficient way to control the transport of monolayer phosphorene-based microstructures.     

二维红外光谱法对肉豆蔻酸相变过程的研究

脂肪酸由于成本低、相变潜热大、热稳定性好的特点,在有机固-液相变材料中应用较多。对脂肪酸进行热分析一般采用热重法（TG）或差示扫描量热法（DSC）得到材料宏观上的热力学性质,但难以对其微观结构变化进行深入探讨。二维红外光谱（2D-IR）在温度扰动的作用下,样品的光谱信号将随之发生动态变化。通过数学处理能够发现样品在相变过程中微观结构的变化。以肉豆蔻酸为例,采用傅里叶红外光谱仪,在4 000～400 cm-1和30～100 ℃温度范围内对肉豆蔻酸进行一系列红外光谱实验。采用二维移动窗口（MW2D）红外光谱技术,对肉豆蔻酸中的CO和O—H键进行分析,发现MW2D测出的肉豆蔻酸熔点与传统的DSC测出的基本一致,且两种化学键显示的热数据具有良好的一致性和稳定性。对光谱数据进行2D-IR分析,结果表明,由于分辨率的提高,一维光谱中单一的重叠吸收峰对应着二维光谱中的多个吸收峰,根据2D-IR的理论知识,推测可能存在二聚体肉豆蔻酸构型向单聚体肉豆蔻酸构型转变的情况。从峰强度和温度的变化关系中发现,升温时CO键和O—H键存在三个变化过程,达到相变温度之前,CO吸收峰强度基本不变,O—H吸收峰强度逐渐下降,说明O—H键偶极矩的变化比CO键更易受温度影响;相变过程中,两者吸收峰强度都显著减弱且O—H吸收峰强度下降幅度更大;达到相变温度之后,可能因O—H形成的分子间氢键,受热导致由强变弱,O—H上的电子云移向CO,导致CO吸收峰强度增大、O—H吸收峰强度减小。同时,结合密度泛函理论,对二维红外光谱的推论进行理论验证,可知存在二聚体肉豆蔻酸向单聚体肉豆蔻酸的转化过程。     

Transition from the Compact to the Dense Phase of Two-Dimensional Polymers

We present a unifying picture of the compact, dense, and dilute phases of two-dimensional polymers. The lattice dependence of the scaling exponents for compact polymers is reconciled with their universality in the dense and dilute cases. In particular, we show that violations of the fully packing constraint in the compact phase can be interpreted as magnetic screening in the associated Coulomb gas, which induces a flow to either the dense or the dilute phase. When more than one flavor of polymers is present the flow away from the compact phase leads to a decoupling of the flavors, and the central charge decreases by an integer. If charge asymmetry develops, the polymer flavors may independently flow to either of the two noncompact phases.     

Phase Transition in CsHSO4 Ferroelastic in a Magnetic Field

JETP Letters - A magnetically induced deceleration of the initial stage of the isothermal phase transition of ferroelastic-superprotonic cesium hydrogen sulfate has been detected. The effect is...     

Laser-Induced Phase Transition in a Monolayer of Polymer Particles Levitating in a Low-Pressure Gas-Discharge Plasma

We report on the results of analysis of the mean kinetic energy and the pair correlation function of polymer particles in a plasma–dust structure under the action of laser radiation. We have observed experimentally the crystal–liquid phase transition in the monolayer of particles levitating in the near-electrode layer of a capacitive high-frequency discharge. The coupling parameter of the dust system has been estimated. The results of analysis of the modification of the polymer dust particle surface after holding in the plasma are considered. We propose an explanation of the phase transition taking into account the role of the photophoretic force in the motion of macroparticles. The effect of the photophoretic force is associated with the modification of the dust particle surface in the plasma, as a result of which the particles can effectively absorb laser radiation.     

Monte Carlo Simulation for the Photoinduced Phase Transition on a Two-Dimensional Stripe-Structure

By means of Monte Carlo simulations for a kinetic Ising model on a two-dimensional square lattice, we demonstrate that a photoinduced phase transition is accomplished more rapidly even for weaker light in a stripe-structure consisting of two kinds of constituent units than in a homogeneous structure. This is due to accelerated nucleation of a final phase in the constituent unit that is relatively close to instability locally.     

Ferroelectric Controlled Spin Texture in Two-Dimensional NbOI_2 Monolayer

The persistent spin helix(PSH) system is considered to have promising applications in energy-conservation spintronics because it supports an extraordinarily long spin lifetime of carriers.Here,we predict that the existence of PSH state in two-dimensional(2 D) ferroelectric NbOI₂ monolayers.Our first-principles calculation results show that there exists Dresselhaus-type spin-orbit coupling(SOC) band splitting near the conduction-band minimum(CBM) of the NbOI₂ monolayer.It is...     

Phase Transition and Superfluid of Photons and Photon Pairs in a Two-Dimensional Optical Microcavity

We analyze the ground-state properties and the excitation spectrum of Bose-Einstein condensates of photons and PPs in a two-dimensional optical microcavity. First, using the variational method, we discuss the ground-state phase transition of the two-component system. We also investigate the energy gap between the ground state and the first excited state. Moreover, by investigating the excitation spectrum, we also illustrate how the superfluid behavior of photons and PPs can be associated with the phase transition of the system.     

Phase Transition and Superfluid of Photons and Photon Pairs in a Two-Dimensional Optical Microcavity

We analyze the ground-state properties and the excitation spectrum of Bose-Einstein condensates of photons and PPs in a two-dimensional optical microcavity. First, using the variational method, we discuss the ground-state phase transition of the two-component system. We also investigate the energy gap between the ground state and the first excited state. Moreover, by investigating the excitation spectrum, we also illustrate how the superfluid behavior of photons and PPs can be associated with the phase transition of the system.     

Deconfinement Phase Transition with External Magnetic Field in the Friedberg-Lee Model

The deconfinement phase transition with external magnetic field is investigated in the Friedberg-Lee model.We expand the potential around the two local minima of the first-order deconfinement phase transition and extract the ground state of the system in the frame of functional renormalization group.By solving the Sow equations we find that the magnetic field displays a catalysis effect and it becomes more difficult to break througii the confinement.     

Phase Transition in Three-Dimensional Noncollinear Magnetic Systems with Additional Two-Fold Degeneracy

JETP Letters - Using Monte Carlo simulations, we investigate the critical behavior in a three-dimensional frustrated helimagnet with an additional two-fold degeneracy, realized in a...     

Two-Dimensional Excitons in Multiple GaN/AlN Monolayer Quantum Wells

JETP Letters - The decay kinetics of low-temperature exciton photoluminescence in a heterostructure with multiple GaN/AlN monolayer quantum wells, which is prepared by molecular beam epitaxy, is...     

Exploitable Magnetic Anisotropy of Magnetic CrBr3 Monolayer

JETP Letters - We investigated the influence of Li and F adsorption on the ferromagnetism and magnetic anisotropy energy of CrBr3 monolayer based on the first-principles calculations. It is...     

范德瓦尔斯磁性材料CrOCl变磁性相变的磁力显微镜研究

近年来,二维范德瓦尔斯磁性材料因为在自旋电子学的应用前景而吸引了广泛的关注.CrOCl是一种范德瓦尔斯磁性材料,理论预言其单层具有高达160 K的居里温度,因此吸引了广泛的关注。为了更好的理解这一材料的磁性,我们利用磁力显微镜研究了CrOCl变磁性相变中磁畴结构随磁场的变化。实验发现,在2K下CrOCl样品表面出现随磁场变化的方格条纹,给出了变磁性相比中反铁磁相和铁磁相竞争的图样,并通过二维快速傅里叶变换证实了CrOCl磁性的各向异性。我们的结果为后续研究CrOCl薄层的磁性提供了参考依据。