International Journal of Modern Physics B

In this study, single-kesterite-phase Cu₂ZnSnS₄ (CZTS) and Cu₂ZnSnSe₄ (CZTSe) nanocrystallines have been synthesized by a simple solvothermal route. Scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet-visible (UV-vis) absorbance and Raman scattering spectroscopy were used to characterize the optical and micro-structure properties of the as-synthesized samples. The bandgap of CZTS could be tuned in a large range by incorporating a few Se atoms. Both the CZTS and CZTSe exhibited the similar temperature dependence of the Raman "A" modes, including a monotonic redshift in peak position and an irregular variation in peak linewidth. Such a behavior might be due to the cumulative effect of thermal expansion and small crystalline sizes.

The modulational instability (MI) of binary condensates with cubic-quintic nonlinearities is investigated. Using a linear stability analysis, a gain of instability is derived then, effects of the quintic nonlinearities on the instability gain are identified. To be precise, attractive intraspecie quintic nonlinearities enhance the instability, while repulsive quintic intraspecie nonlinearities soften the instability. Besides, small attractive and large repulsive quintic inter-species nonlinearities increase the instability. Numerical experiments quite well corroborate the analytical predictions. Further numerical results show effects of the cubic and the quintic nonlinearities on the propagation of trains of bright solitons generated.

In this paper, based on Lyapunov stability theory, a novel scheme is proposed to explore the lag synchronization of Coullet system. Via back stepping method, the scheme needs only a single controller and the sufficient condition of synchronization is derived. To illustrate the effectiveness of the proposed scheme, some numerical simulations are presented.

This paper further investigates the adaptive full state hybrid projective synchronization (FSHPS) of hyper-chaotic systems — CYQY system with fully unknown parameters and perturbations. Based on the Lyapunov stability theory, adaptive controllers and updating laws of parameters can be designed for achieving the FSHPS of the CYQY hyper-chaotic systems with the same and different structures. Two groups numerical simulations are provided to verify the effectiveness of the proposed scheme.

Former results for a tight-binding (TB) model of CuO planes in La₂CuO₄ are reinterpreted here to underline their wider implications. It is noted that physical systems being appropriately described by the TB model can exhibit the main strongly correlated electron system (SCES) properties, when they are solved in the HF approximation, by also allowing crystal symmetry breaking effects and noncollinear spin orientations of the HF orbitals. It is argued how a simple 2D square lattice system of Coulomb interacting electrons can exhibit insulator gaps and pseudogap states, and quantum phase transitions as illustrated by the mentioned former works. A discussion is also presented here indicating the possibility of attaining room temperature superconductivity, by means of a surface coating with water molecules of cleaved planes of graphite, being orthogonal to its c-axis. The possibility that 2D arrays of quantum dots can give rise to the same effect is also proposed to consideration. The analysis also furnishes theoretical insight to solve the Mott–Slater debate, at least for the La₂CuO₄ and TMO band structures. The idea is to apply a properly noncollinear GW scheme to the electronic structure calculation of these materials. The fact is that the GW approach can be viewed as a HF procedure in which the screening polarization is also determined. This directly indicates the possibility of predicting the assumed dielectric constant in the previous works. Thus, the results seem to identify that the main correlation properties in these materials are determined by screening. Finally, the conclusions also seem to be of help for the description of the experimental observations of metal-insulator transitions and Mott properties in atoms trapped in planar photonic lattices.

We present a study of the influence of annealing and doping on the electrical properties of few-layer (FL) MoS₂ films on Si and quartz substrates deposited using a self-designed metal sulfide chemical vapor deposition (MSCVD) system. FL MoS₂ slices obtained through MSCVD, in the size range of 50–200 nm, were found to be uniformly scattered on the substrates. The conductivity and mobility of these films are greatly enhanced after annealing at 650–850°C. The largest mobility measured for pure MoS₂ on quartz substrate is 6.4×10³cm²/Vs, almost two orders of magnitude larger than that of bulk MoS₂ (500 cm²/Vs). We deduce that the superior charge carrier mobility in our sample is mainly attributed to reduced phonon scattering because of a lower carrier density (10¹⁰-10¹¹ cm^-2) compared to previously documented values (10¹²-10¹³cm^-2). Additionally, the conductivity and carrier concentration of FL MoS₂ films were enhanced by about two orders of magnitude compared to those of the as-grown films doped with Cu, Na and Ag ions but not doped with B ions. The films doped with Na and Ag exhibit characteristic p-type conductivity, while those doped with Cu and B exhibit n-type conductivity. Moreover, the MoS₂/Si heterojunction exhibited good rectification characteristics and excellent conductivity, indicating that the FL MoS₂ films will find many applications in high-efficiency nanodevices.

In this paper, the effect of high-frequency laser fields on a symmetric Modified-Pöschl–Teller (MPT) potential is studied by the laser dressing parameter. The magnitude of the laser dressing parameter is determined by the intensity and the frequency of the laser field. The well depth decreases with increasing laser dressing parameter. The symmetric MPT potential becomes asymmetric under an applied electric field. In this well the optical absorption coefficients, the changes in refractive indices, and the second-order susceptibilities such as the nonlinear optical rectification (NOR) and the second harmonic generation (SHG) are calculated using the density matrix method. The nonlinear susceptibilities are found to get reduced in the laser-driven potential.

In conventional community detecting algorithms, the community number is always a bypass product and cannot be estimated before partitioning. Since partitioning large scale and dynamic complex networks takes exhausting computation, the community number sometimes can be a terminal condition of iterations or a preset optimal parameter for speeding up partitioning algorithms. This paper assumes that communities are organized around the center of core nodes in a scale-free network. A separability function is built to dichotomize nodes into two classes and the class of large degree nodes is selected as the core node candidate set. An improved shortest path seeking algorithm is applied to remove the closest neighbors of a specific core node. The number of remaining core nodes is then the estimated number of communities. Experiments of real world scale-free networks and computer generated networks show that the results are very close to the well-proven results.

The structural, electronic thermodynamic and thermal properties of Ba_xSr_1-xTe ternary mixed crystals have been studied using the ab initio full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). In this approach, the Perdew–Burke–Ernzerhof-generalized gradient approximation (PBE-GGA) was used for the exchange-correlation potential. Moreover, the recently proposed modified Becke Johnson (mBJ) potential approximation, which successfully corrects the band-gap problem was also used for band structure calculations. The ground-state properties are determined for the cubic bulk materials BaTe, SrTe and their mixed crystals at various concentrations (x = 0.25, 0.5 and 0.75). The effect of composition on lattice constant, bulk modulus and band gap was analyzed. Deviation of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for the ternary Ba_xSr_1-xTe alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing, ΔH_m as well as the phase diagram. It was shown that these alloys are stable at high temperature. Thermal effects on some macroscopic properties of Ba_xSr_1-xTe alloys were investigated using the quasi-harmonic Debye model, in which the phononic effects are considered.