International Journal of Modern Physics B

In this paper, spin-polarized density functional calculations on the structural, electronic, optical and magnetic properties of the zincblende structure of the ${\mathrm{\text{Zn}}}_{1-x}{\mathrm{\text{V}}}_x\mathrm{\text{S}}$ and ${\mathrm{\text{Cd}}}_{1-x}{\mathrm{\text{V}}}_x\mathrm{\text{S}}$ alloys at $x=0.25$ in the ferromagnetic (FM) ordering has been investigated. The study is accomplished using the full-potential (FP) linearized augmented plane wave plus local orbital (LAPW$+$lo) self-consistent scheme of calculations. To incorporate the exchange correlation component in the total energy calculations of the crystal, Perdew–Burke and Ernzerhof (PBE) parameterization for the generalized gradient approximation (GGA) and GGA$+$U are employed. Basically, for both alloys, to address their structural properties, we calculated their equilibrium lattice constants, bulk moduli as well as pressure derivatives. In general, from the analysis of the obtained electronic band structure of these alloys, the half-metallic nature of ${\mathrm{\text{Zn}}}_{0.75}{\mathrm{\text{V}}}_{0.25}\mathrm{\text{S}}$ and nearly half-metallic nature of the ${\mathrm{\text{Cd}}}_{0.75}{\mathrm{\text{V}}}_{0.25}\mathrm{\text{S}}$ alloy are demonstrated. The plotted density of states (DOS) curves project spin-exchange splitting energy ${\mathrm{\Delta }}_x(d)$ and ${\mathrm{\Delta }}_x(pd)$ as generated by V-3d states. It has been clearly evident that the effective potential results for the spin-down case are more striking than for the spin-up case. In order to describe the magnetic behavior of these alloys, the exchange constants $N_{0\alpha }$ (valence band) and $N_{0\beta }$ (conduction band) as well as the magnetic moment values are estimated. The calculated results of the magnetic moment show that the main source in the reduction of the local magnetic moment of V in the alloys in comparison with its free value is a $p$–$d$ orbital hybridization and partial transfer to nonmagnetic sites of (Zn, S) and (Cd, S) in ${\mathrm{\text{Zn}}}_{0.75}{\mathrm{\text{V}}}_{0.25}\mathrm{\text{S}}$ and ${\mathrm{\text{Cd}}}_{0.75}{\mathrm{\text{V}}}_{0.25}\mathrm{\text{S}}$ alloys. In addition, a study concerning optical properties, such as the refractive index, reflectivity and absorption coefficients is performed to determine their potential for optical and optoelectronic devices.

Electron–positron pair-production process is observed in polychromatic light oscillating electric fields. A quantum kinetic theory is presented to obtain the pair-production rate and the momentum information. Oscillating structures of the particle yield and the odd–even structure of the momentum–frequency spectrum are depicted. The roles of the phase factor and the frequency multiplication are analyzed. We find the odd–even structures are remained in the triple-frequency field.

We show that it is possible to model two-body resonant interactions at low energy with a class of finite-range potentials based on the methods of Jost and Kohn. These potentials are expressed in terms of the effective range $r_0$ and the $s$-wave scattering length $a_s$. We derive continuum solutions of these potentials. By writing $V_{\pm }(r)=V_0(r)+V_{\pm }^{ϵ}(r)$, where the sign $+(-)$ refers to positive(negative) scattering length, $V_0(r)$ is of the form of Pöschl–Teller potential and $V_{\pm }^{ϵ}$ is expressed as a power series of the small parameter $ϵ={(\sqrt{1-2r_0/a_s})}^{-1}-1$ when $a_s$ is large, we derive Green’s function of $V_0(r)$. Using the Green’s function, solutions of $V_{\pm }(r)$ for $\left|a_s\right|\gg r_0$ can be obtained numerically by treating $V_{\pm }^{ϵ}(r)$ as a perturbation. We describe the threshold behavior of scattering phase shift for $V_0(r)$. This study may be important for developing a better understanding of physics of strongly interacting ultracold atomic gases with tunable interactions.

How to identify community structure in complex network is of theoretical significance, which relates to help to analyze the network topology and understand the network works. Determining the optimal number of communities is a nontrivial problem in detecting community structure. In this paper, we propose a novel method for detecting the optimal number of communities. Based on the local random walk (LRW) measurement, the distance index between each pair of nodes of a network is calculated firstly. Then the optimal number of communities can be found based on the idea that community centers are characterized by a higher density than their neighbors and by a relatively large distance from nodes with higher densities. The experimental results show that the method is effective and efficient in both artificial and real-world networks.

Molecules have at least one nontrivial topological property in common: their minimal surfaces of finite flux. This is why they are stable aggregates of atoms mutually engaged to varying degrees via Coulombic and exchange interactions in fealty to quantum mechanics on otherwise passive nuclear scaffolds. Isolated atoms do not have minimal surfaces but they do undergo exchange interactions. All surfaces implicitly defined by a molecule’s charge density are shown to have zero mean curvature and are consequently minimal surfaces. This finding extends to any potential of a molecule. The minimal surface is of importance in that it is indicative of a vanishing mean curvature whose measurement serves as a way of gauging the charge density or electrostatic potential’s local reliability, a quality assurance protocol absent in conventional crystallography but available to scanning force microscopy. The smaller the mean curvature of an atom, the more bonded is that atom in a molecule. The basis for this discovery is that implicit surfaces admit finite flux to cross them regardless of atomic affiliation, thus engendering exchange, correlation, and chemical bonding between the atoms in the underlying nuclear framework of a molecule. Finite flux in the charge density is a necessary condition for chemical bonding and the stability of molecules and is what makes the electron localization function (ELF) and the exchange-correlation functional (BLYP) useful.

We study Hall and Nernst transports in monolayer MoS₂ based on Green’s function formalism. We have derived analytical results for spin and valley Hall conductivities in the zero temperature and spin and valley Nernst conductivities in the low temperature. We found that tuning of the band gap and spin-orbit splitting can drive system transition from spin Hall insulator (SHI) to valley Hall insulator (VHI). When the system is subjected to a temperature gradient, the spin and valley Nernst conductivities are dependent on Berry curvature.

Community structure is an important and universal topological property of many complex networks such as social and information networks. The detection of communities of a network is a significant technique for understanding the structure and function of networks. In this paper, we propose an algorithm based on distributed learning automata for community detection (DLACD) in complex networks. In the proposed algorithm, each vertex of network is equipped with a learning automation. According to the cooperation among network of learning automata and updating action probabilities of each automaton, the algorithm interactively tries to identify high-density local communities. The performance of the proposed algorithm is investigated through a number of simulations on popular synthetic and real networks. Experimental results in comparison with popular community detection algorithms such as walk trap, Danon greedy optimization, Fuzzy community detection, Multi-resolution community detection and label propagation demonstrated the superiority of DLACD in terms of modularity, NMI, performance, min-max-cut and coverage.

In this paper, we have studied the effect of external magnetic field in the co-existing phase of superconducting and antiferromagnetism (AFM) of rare earth nickel borocarbides. The AFM in these systems might have originated due to both localized “f” electrons as well as itinerant electrons which are responsible for conduction. On the other hand, superconductivity (SC) is due to spin density wave, arising out of Fermi surface instability. The AFM order is mostly influenced by hybridization of the “f” electron with the conduction electron. Here, we have obtained the dependence of superconducting energy gap as well as staggered magnetic field on temperature T and energy ${ϵ}_k$ in a framework based on mean field Hamiltonian using double time electron Green’s function. We have shown in our calculation the effect of external magnetic field on superconducting and antiferromagnetic order parameters for ${\mathrm{\text{YNi}}}_2{\mathrm{\text{B}}}_2\mathrm{\text{C}}$ in the presence of hybridization. The ratio of the calculated effective gap and $T_C$ is close to BCS value which agrees quite well with experimental results.

Improve beam quality of laser proton acceleration using a funnel-shaped-hole target is demonstrated through particle simulations. When an intense short pulse laser illuminates a thin foil target with a hole at the rear surface, the proton beam divergence is suppressed compared with that obtained in a traditional flat target. In this paper, a funnel-shaped-hole target is proposed to improve the proton beam quality. Using two-dimensional particle-in-cell (PIC) simulations, three different shapes of target (funnel-shaped-hole target, cylinder-shaped-hole target and flat target) are simulated and compared. The funnel-shaped hole in the rear surface of the target helps to focus the electron cloud significantly and improve the maximum proton energy and suppress the proton beam divergence. Different thicknesses of the new target are also simulated, and the effects of thickness on the divergence angle and proton spectra are investigated. The optimal size of the new target is obtained and the quality of the proton beam is improved significantly. The funnel-shaped-hole target serves as a new method to improve the proton beam quality in laser–plasma interactions.