International Journal of Modern Physics B

In this paper, electronic and optical properties of GaN/InN core/shell nanowires (CSNWs) have been theoretically investigated through the first principles calculations. The binding energy of In and N atoms on surface of six crystal planes along the $z$-axis of GaN nanowires are all negative, which indicate that In and N atoms can be effectively deposited on the surface of GaN nanowires and preparing GaN/InN CSNWs is feasible theoretically. Calculation results of electronic properties indicate that the core/shell ratio and diameter of GaN/InN CSNWs have significant effect on the band structure, bandgap can be effectively adjusted when keeping the number of GaN layers unchanged and changing the number of InN layers. Moreover, with the increase in the number of InN layers, the absorption spectrum of GaN/InN CSNW has significant redshift and few weak absorption peaks appear in the visible light region.

Density Functional Theory (DFT) is used to investigate the phonon properties of CoFeCrZ (Z=Al, Si, Ga, Ge) equiatomic Quaternary Heusler Alloys. These alloys crystallize in face centered cubic (FCC) structure and have three crystal structures Y-Type I, Y-Type II and Y-Type III on the basis of their atomic positions. For CoFeCrZ (Z=Al, Si, Ga, Ge), Y-Type I is the most stable structure found in the literature, so phonon dispersion curves for this structure are obtained with the help of norm-conserving pseudo potentials in Quantum ESPRESSO. Absence of negative frequencies in phonon dispersion curves proves the dynamical stability of all these alloys. Phonon dispersion curves are further used to obtain Reststrahlen band, a region where light reflects 100%. The calculated Reststrahlen bands for CoFeCrAl, CoFeCrSi, CoFeCrGa and CoFeCrGe are 4.179 THz ($\mathrm{\Delta }\lambda =71.73\mu$m), 4.30 THz ($\mathrm{\Delta }\lambda =69.71\mu$m), 3.35 THz ($\mathrm{\Delta }\lambda =89.49\mu$m) and 3.05 THz ($\mathrm{\Delta }\lambda =98.99\mu$m), respectively. These obtained values of Reststrahlen bands for CoFeCrZ (Z=Al, Si, Ga, Ge) lie within the far infra-red (FIR) region, and can be used in sensing, imaging and optoelectronic devices.

In this work, the mixed system composed of Zn₂GeO₄: Mn and MgGeO₃: Mn, Eu was synthesized by the high temperature solid phase method. Under the external excitation, visual color of samples was yellow. However, after the excitation was completed, visual color turned to be red. From luminescence spectrum, it was found that Zn₂GeO₄: Mn emitted green fluorescence of 534 nm under the excitation of 375 nm light. At the same time, MgGeO₃: Mn, Eu emitted both fluorescence and persistent luminescence (PersL) of 668 nm. Moreover, the properties of PersL present samples were superior to other red PersL materials. Fine band structures from density functional theory (DFT) indicated that there were different luminescent mechanisms of Zn₂GeO₄: Mn and MgGeO₃: Mn, Eu. When Zn₂GeO₄: Mn was excited, electron transitioned from VB to CB directly. Through CB, the electron was captured by the ⁴T₂(D) of Mn ion, then the electron jumped from ⁴T₂(D) to VB and recombined at once with the previous hole and emitted a 534 nm photon. When MgGeO₃: Mn, Eu was excited, electron transitioned from ⁶A₁(S) of Mn ion to CB and left a hole. Through CB, electron was captured by ⁷F₆ levels of Eu${}^{3+}$ and remained metastable for a long time, which slowed down the recombined rate between electron and hole. Under thermal stimulation, the captured electron returned to CB from ⁷F₆ levels and was recaptured by the ⁴T₂(D) of Mn. The electron transitioned down toward ⁶A₁(S) and recombined with the hole immediately, then emitted a photon with 668 nm.

The molecular dynamics simulation has been performed to study the effects of temperature on interdiffusion of Ni–Zr system. The simulated results indicate that the thickness of Ni/Zr diffusion layer increased with increasing diffusion time, and interdiffusion results in disordered or amorphization in the diffusion zone. During the diffusion process, Ni atoms diffuse crossing the interface more easily and deeply into Zr side than Zr atoms into Ni side. The activation energies of Ni and Zr are 1.25 and 1.28 eV for Ni(100)//Zr(0001) interface, 1.33 and 1.42 eV for Ni(110)//Zr(0001) interface at the temperature range of 950–1100 K, respectively. The microscopic diffusion mechanisms for Ni atoms in Zr lattice have been studied, and the results show that the most possible diffusion mechanism is the interstitial hopping mechanism, while for Zr diffusing in Ni, the vacancy diffusion mechanism is favored. The interdiffusion for case of Ni(110)//Zr(0001) interface is more easy than that of Ni(100)//Zr(0001) interface due to the lower surface energy for the former. In the diffusion zone of Ni–Zr, some typical clusters have been identified, which are similar to those extracted from the Ni–Zr intermetallic compounds, and which are generally consistent with the experimental observations in diffusion couples.

We have applied the first-principles method to predict the phase stability, elastic and thermodynamic properties of ternary (AlCrFe, AlCrNi, CrFeNi and AlFeNi) and quaternary (AlCrFeNi) medium-entropy alloys (MEAs). Both body-centered cubic (BCC) and face-centered cubic (FCC) disordered structures are described using the special quasi-random structures (SQSs) technique. AlCrFe, AlCrNi and AlCrFeNi are favorable in single BCC structures, while CrFeNi is likely to form a single FCC structure. Addition of Ni help stabilizes AlCrFeNi quaternary MEAs. Al and Cr addition are in favor of the formation of BCC AlCrFeNi. Addition of Al, Cr and Ni reduce the resistance to volume deformation for quaternary AlCrFeNi due to the effect of the average number of $d$-electrons. The ternary MEAs have better resistance to shear deformation and elastic stiffness than quaternary AlCrFeNi. In addition, all the considered MEAs embody elastic anisotropy and AlCrFeNi are predicted to be ductile behavior. Finally, volumetric thermal expansion coefficient, constant volume heat capacity, vibrational and electronic entropy, and Helmholtz free energies of stable BCC AlCrFeNi, BCC AlCrFe, BCC AlCrNi and FCC CrFeNi are calculated using the Debye–Grüneisen model in temperature ranging from 0 to 1200 K to elucidate the relationships between thermodynamic parameters and temperature.

In this paper we study the nonlocal reductions for the non-isospectral Ablowitz-Kaup-Newell-Segur equation. By imposing the real and complex nonlocal reductions on the non-isospectral Ablowitz-Kaup-Newell-Segur equation, we derive two types of nonlocal non-isospectral nonlinear Schrödinger equations, in which one is real nonlocal non-isospectral nonlinear Schrödinger equation and the other is complex nonlocal non-isospectral nonlinear Schrödinger equation. Of both of these two equations, there are the reverse time nonlocal type and the reverse space nonlocal type. Soliton solutions in terms of double Wronskian to the reduced equations are obtained by imposing constraint conditions on the double Wronskian solutions of the non-isospectral Ablowitz-Kaup-Newell-Segur equation. Dynamics of the one-soliton solutions are analyzed and illustrated by asymptotic analysis.

The structures with different compositions of the binary Mg–Y alloys have been predicted by first-principles calculations combined with an unbiased Crystal structure Analysis by Particle Swarm Optimization (CALYPSO) structure searching method. The two already known stoichiometries alloys of Mg₁Y₁ with Pm-$3m$ symmetry and Mg₃Y₁ with Fm-$3m$ are confirmed, and a new stoichiometry alloy of Mg₁Y₃ with $P2/m$ symmetry is proposed. The dynamical and mechanical stabilities for the three alloys at different pressures are investigated by phonon spectra and mechanical stability criteria, respectively. Subsequently, the bulk modulus, shear modulus, Young’s modulus, the brittleness/ductile behavior, the elastic anisotropy as well as Vickers hardness for the three alloys at 0 GPa are discussed in detail. The results show that the Mg₁Y₁, Mg₃Y₁ and Mg₁Y₃ alloys improve the hardness and stiffness compared with pure Mg, and Mg₁Y₃ alloy is of the best ductility in the three alloys. Meanwhile, the three alloys exhibit anisotropic. Moreover, the thermodynamic properties, such as Debye temperature, heat capacity at constant volume, entropy and Helmholtz free energy for the three stable alloys, are predicted and discussed.

In this present article, the new $(2+1)$-dimensional modified Calogero-Bogoyavlenskii-Schiff (mCBS) equation is studied. Using the Lie group of transformation method, all of the vector fields, commutation table, invariant surface condition, Lie symmetry reductions, infinitesimal generators and explicit solutions are constructed. As we all know, an optimal system contains constructively important information about the various types of exact solutions and it also offers clear understandings into the exact solutions and its features. The symmetry reductions of $(2+1)$-dimensional mCBS equation is derived from an optimal system of one-dimensional subalgebra of the Lie invariance algebra. Then, the mCBS equation can further be reduced into a number of nonlinear ODEs. The generated explicit solutions have different wave structures of solitons and they are analyzed graphically and physically in order to exhibit their dynamical behavior through 3D, 2D-shapes and respective contour plots. All the produced solutions are definitely new and totally different from the earlier study of the Manukure and Zhou (Int. J. Mod. Phys. B 33, (2019)). Some of these solutions are demonstrated by the means of solitary wave profiles like traveling wave, multi-solitons, doubly solitons, parabolic waves and singular soliton. The calculations show that this Lie symmetry method is highly powerful, productive and useful to study analytically other nonlinear evolution equations in acoustics physics, plasma physics, fluid dynamics, mathematical biology, mathematical physics and many other related fields of physical sciences.

Molten salts constitute one kind of PCMs (Phase Change Materials) widely used in concentrating solar power facilities for heat storage and heat transfer. This paper aims to simulate nanofluid PCMs with molecular dynamics method. Concretely, the thermophysical properties of a nanofluid of KNO₃ doped with SiO₂ nanoparticle are investigated by equilibrium and nonequilibrium molecular dynamics simulations. For the first time, these properties of a nanofluid in the family of PCMs are calculated. The density, thermal expansion coefficient, specific heat capacity, thermal conductivity, and viscosity are characterized as functions of the SiO₂ nanoparticle concentration. The effect of the SiO₂ nanoparticle size on the nanofluid’s properties is also investigated. The simulation results present an enhancement of the thermophysical properties, especially for the specific heat capacity, in good agreement with the existing experimental results on a representative nanofluid PCM, and open prospects for the understanding of microscopic mechanism leading to such enhancements.

In this paper, a new state called superposition of multiple-photon-added two-mode squeezed vacuum state (SMPA-TMSVS) is introduced by adding the multiple photons to both modes of a two-mode squeezed vacuum state (TMSVS). We explicitly investigate the degree of quantum entanglement, the Einstein–Podolsky–Rosen (EPR) correlation and the quantum steering in the SMPA-TMSVS. The results show in the SMPA-TMSVS that the degree of entanglement and the EPR correlation can be enhanced by nonlocal adding photons to a TMSVS. The quantum steering appears in the SMPA-TMSVS in case the superposition of single-photon addition $h=k=1$, in which mode $a$ can steer mode $b$. By using the SMPA-TMSVS as an entangled resource, the quantum teleportation process is studied in detail based on the Vaidman–Braunstein–Kimble (VBK) protocol.

In this paper, the impurity states in square, parabolic and V-shaped quantum wells (QWs) are calculated by the plane wave method under the theoretical framework of effective mass envelope function approximation. In different shaped QWs, the impurity binding energies in 1s-like state and 2p-like state have the same trend with the increase of QW width. However, the transition energies of impurity states between 1s-like state and 2p-like state in three shaped QWs are different. When the width of QW is fixed, the transition energy in square QW is the minimum and that in V-shaped QW is the maximum. The effect of electric field is larger for the on-center donor impurity. The effect of electric field on the impurity states is the largest in square QW and the smallest in V-shaped QW.

Due to the large difference in mode size and effective-index mismatch between the optical fiber and the waveguides on the photonic integrated circuits, it is a big challenge to efficiently couple light into thin semiconductor waveguides. In this paper, a taper plasmonic coupler is presented to couple fiber light into an Si waveguide. The taper plasmonic coupler structure is optimized, and the alignment tolerance of the gap, the lateral offset and the vertical offset between coupler and Si waveguide are studied. Numerical simulation shows that the coupler changes the single mode fiber light to multimode light at its input port section, while at its output port section, the coupler turns the multimode light back to a single mode light, and finally couples this light to Si waveguide. The maximum couple efficiency is 86.8% in $25\mu \mathrm{\text{m}}$ effective coupler length.

For a variable-coefficient Korteweg–de Vries equation in a lake/sea, two-layer liquid, atmospheric flow, cylindrical plasma or interactionless plasma, in this paper, we derive the bilinear Bäcklund transformation, non-isospectral Ablowitz–Kaup–Newell–Segur system and infinite conservation laws for the wave amplitude under certain constraints among the external force, dissipation, nonlinearity, dispersion and perturbation.

In the current study, we instigate the four-dimensional nonlinear modified Zakharov–Kuznetsov (NLmZK) equation. The NLmZK equation guides the attitude of weakly nonlinear ion-acoustic waves in a plasma comprising cold ions and hot isothermal electrons in the presence of a uniform magnetic field. Two different methods are used, namely the sine-Gordon expansion method (SGEM) and the $(1/G^{\prime })$-expansion method to the proposed model. We have successfully constructed some topological, non-topological, and wave solutions. In addition, the 2D, 3D, and contour graphs of the solutions are also plotted under the choice of appropriate values of the parameters.