International Journal of Modern Physics B

Ising model with competing nearest–neighbors (NN) and prolonged next–nearest–neighbors (NNN) interactions on a Cayley tree has long been studied, but there are still many problems untouched. This paper tackles new Gibbs measures of Ising–Vannimenus model with competing NN and prolonged NNN interactions on a Cayley tree (or Bethe lattice) of order three. By using a new approach, we describe the translation-invariant Gibbs measures (TIGMs) for the model. We show that some of the measures are extreme Gibbs distributions. In this paper, we try to determine when phase transition does occur.

In the present work, initially, a mixed-three-spin (1/2,1,1/2) cell of a mixed-$N$-spin chain with Ising-XY model is introduced, for which pair spins (1,1/2) have Ising-type interaction and pair spins (1/2,1/2) have both XY-type and Dzyaloshinskii–Moriya (DM) interactions together. An external homogeneous magnetic field $B$ is considered for the system in thermal equilibrium. Integer-spins have a single-ion anisotropy property with coefficient $\zeta$. Then, we investigate the quantum entanglement between half-spins (1/2,1/2), by means of the concurrence. Classical correlation (CC) for this pair of spins is investigated as well as the concurrence and some interesting temperature, the magnetic field and the DM interaction properties are expressed. Moreover, single-ion anisotropy effects on the correlation between half-spins is verified. According to the verifications based on the communication channels category by Rossini, Giovannetti and Fazio [D. Rossini, V. Giovannetti and R. Fazio, Int. J. Quantum Inf. 5, 439 (2007)], we theoretically consider such tripartite spin model as an ideal quantum channel, then calculate its information transmission rate and express some differences in behavior between this suggested model and introduced simple models in the previous works (chains without spin integer and DM interaction) from information transferring protocol point of view.

This work introduces an analysis of the relationship of first-principles calculations based on DFT method with the results of free particle model for ring-shaped aromatic molecules. However, the main aim of the study is to reveal the angular electronic band structure of the ring-shaped molecules. As in the case of spherical molecules such as fullerene, it is possible to observe a parabolic dispersion of electronic states with the variation of angular quantum number in the planar ring-shaped molecules. This work also discusses the transition probabilities between the occupied and virtual states by analyzing the angular electronic band structure and the possibility of ring currents in the case of spin angular momentum (SAM) or orbital angular momentum (OAM) carrying light. Current study focuses on the benzene molecule to obtain its angular electronic band structure. The obtained electronic band structure can be considered as a useful tool to see the transition probabilities between the electronic states and possible contribution of the states to the ring currents. The photoinduced current due to the transfer of SAM into the benzene molecule has been investigated by using analytical calculations within the frame of time-dependent perturbation theory.

Vacancy plays a crucial role in mechanical properties of transition metal borides (TMBs). However, the influence of vacancy on hardness of TMBs is unknown. In this paper, the relationship between boron vacancy and mechanical properties of CrB₄ is investigated by first-principle calculations. Two different vacancies including boron monovacancy (MV) and boron bivacancy (BV) are considered. We find that CrB₄ with boron MV is more stable than that of boron BV. The removed atom weakens the deformation resistances, and reduces the elastic stiffness and hardness. The calculated shear modulus, Young’s modulus and theoretical hardness of boron MV are larger than that of boron BV. The reason is that the removed atom weakens the localized hybridization between B and B atoms, and damages the 3D-network B–B covalent bond. However, the bulk modulus of B${}_{\mathrm{\text{-BV4}}}$ is slightly larger than that of perfect CrB₄. This reason is attributed to the formation of triangular pyramid bonding in B${}_{\mathrm{\text{-BV4}}}$ vacancy.

Correlations in quantum fluids such as liquid ³He continue to be of high interest to scientists. Based on this prospect, the present work is devoted to study the effects of spin–spin correlation function on the thermodynamic properties of polarized liquid ³He such as pressure, velocity of sound, adiabatic index and adiabatic compressibility along different isentropic paths, using the Lennard–Jones potential and employing the variational approach based on cluster expansion of the energy functional. The inclusion of this correlation improves our previous calculations and leads to good agreements with experimental results.

We investigate on the infrared (IR) optoelectronic properties in short-period InAs/GaSb type-II superlattices (SLs) by a modified eight-band $K\cdot P$ model. The electronic mini-band structures for such SLs are evaluated by the modified eight-band $K\cdot P$ model, incorporating the microscopic interface effect. We find that with varying the values around 20/25 Å for the InAs/GaSb layer widths, the tunable mid-IR bandgaps can be achieved effectively. The SL bandgap from 275 to 346 meV can be achieved by decreasing the InAs layer thickness from 23 to 17 Å at a fixed GaSb layer thickness of 24 Å, or from 254 to 313 meV by increasing the GaSb layer thickness from 18 to 27 Å at a fixed InAs layer thickness of 21 Å. Correspondingly the optical absorptions in such systems can be tuned evidently. Our theoretical results are in good agreement with experimental data over a series of SL samples. This study confirms further that short-period InAs/GaSb type-II SLs are of great importance for IR applications.

Traveling waves of a class of higher-order traffic flow models with viscosity are studied with the reduction perturbation method, which leads to the well-known Kortweg–de Vries equation and the approximate solitary wave solution to the model. The fifth-order accuracy weighted essentially nonoscillatory scheme is adopted for comparison between the analytical and numerical results. The numerical tests show that the solitary wave evolves with little deformation of its profile and that a globally perturbed equilibrium traffic state is able to evolve into a profile similar to that of a solitary wave, which is identified by the same total number of vehicles on the ring road. These results are compared with those in the literature and demonstrate that the approximation to the model is more accurate.

We report the thermodynamic properties of cuprate superconductors YBa₂Cu₃O${}_{6+x}$, with $x$ ranging from underdoped ($x=0.55$) to optimally doped ($x=0.9$) regions. We model cuprates as a boson–fermion gas mixture immersed in a layered structure, which is generated via a Dirac-comb potential applied in the perpendicular direction to the CuO₂ planes, while the particles move freely in the other two directions. The optimal system parameters, namely, the planes’ impenetrability and the paired-fermion fraction, are obtained by minimizing the Helmholtz free energy in addition to fixing the critical temperature $T_c$ to its experimental value. Using this optimized scheme, we calculate the entropy, the Helmholtz free energy and the specific heat as functions of temperature. Additionally, some fundamental properties of the electronic specific heat are obtained, such as the normal linear coefficient $\gamma (T_c)$, the quadratic $\alpha$ term and the jump height at $T_c$. We reproduce the cubic ${\beta }_l$ term of the total specific heat for low temperatures. Also our multilayer model inherently brings with it the mass anisotropy observed in cuprate superconductors. Furthermore, we establish the doping value beyond which superconductivity is suppressed.

Achieving outstanding physical and optical properties of borosulfophosphate glasses via controlled doping of rare earth ions is the key issue in the fabrication of new and highly-efficient glass material for diverse optical applications. Thus, the effect of replacing P₂O₅ by Dy₂O₃ on the physical and optical properties of Dy${}^{3+}$-doped lithium-borosulfophosphate glasses with chemical composition of 15Li₂O–30B₂O₃–15SO₃–$(40-x)$P₂O₅–$x$Dy₂O₃ (where 0.0 mol.% $\le x\ll 1.0$ mol.%) has been investigated. The glass samples were synthesized from high-purity raw materials via convectional melt-quenching technique and characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectrometry (EDX), density and UV–vis–NIR absorption measurements. The amorphous nature of the prepared glass samples was confirmed by XRD patterns whereas the EDX spectrum depicts elemental traces of O, C, B, S, P and Dy. The physical parameters such as density, refractive index, molar volume, polaron radius and field strength were found to vary nonlinearly with increasing Dy₂O₃ concentration. UV–vis–NIR absorption spectra revealed seven absorption bands with most dominant peak at 1269 nm (⁶H${}_{15/2}\to {}^6$F${}_{11/2}{+}^6$H${}_{9/2}$). From the optical absorption spectra, the optical bandgap and Urbach’s energy have been determined and are related with the structural changes occurring in these glasses with increase in Dy₂O₃ content. Meanwhile, the bonding parameters ($\delta$) evaluated from the optical absorption spectra were found to be ionic in nature. The superior features exhibited by the current glasses nominate them as potential candidate for nonlinear optical applications.

To understand time-evolving networks, researchers should not only concentrate on the community structures, an essential property of complex networks, in each snapshot, but also study the internal evolution of the entire networks. Temporal communities provide insights into such mechanism, i.e., how the communities emerge, expand, shrink, merge, split and decay over time. Based on the symmetric nonnegative matrix factorization (SNMF), we present a dynamic model to detect temporal communities, which not only could find a well community structure in a given snapshot but also demands the results bear some similarity to the partition obtained from the previous snapshot. Moreover, our method can handle the situation that of the number of community changes in the networks. Also, a gradient descent algorithm is proposed to optimize the objective function of the model. Experimental results on both the synthetic and real-world networks indicate that our method outperforms the state-of-art methods for temporal community detection.

In this paper, we have developed relationship to predict temperature dependence of elastic constants for geophysical minerals by using a formulation for volume dependence of isothermal Anderson–Grünesien parameter which is valid up to extreme compression limit $P\to \infty$ or $V\to 0$. An alternative formulation based on thermal pressure or thermal energy has also been used for determining elastic constants as a function of temperature. The basic idea used in this study is to generalize the expression of bulk modulus for determining temperature dependence of elastic constants. The results thus obtained for MgO, CaO, Mg₂SiO₄ and Al₂O₃ from the two different methods are very close to each other and also experimental data. The good agreement reveals the validity of the formulations given in this study.

Thermodynamic relations like the Gibbs–Duhem are valid from the lowest to the highest temperatures. But they cannot by themselves provide any specific temperature behavior of thermodynamic functions like the chemical potential. In this work, we show that if some general conditions are attached to the Gibbs–Duhem equation, it is possible to obtain the low temperature form of the chemical potential for the ideal Fermi and Bose gases very directly.