International Journal of Modern Physics B

The dynamics of a quasi-two-dimensional electron system (q2DES) in the presence of a tilted magnetic field is reconsidered employing the thin-layer method. We derive the effective equations for relativistic and nonrelativistic q2DESs. Through a perturbative expansion, we show that while the magnetic length is much greater than the confinement width, the in-plane magnetic field only affects the particle dynamics through the spin. Therefore, effects due to an in-plane magnetic vector potential reported previously in the literature for 2D quantum rings, 2D quantum dots and graphene are fictitious. In particular, the so-called pseudo chiral magnetic effect recently proposed in graphene is not realistic.

The influence of erbium on physical and optical properties of calcium sulfate ultra-phosphate glass was investigated using conventional melt quench process. Selected samples of composition 20CaSO₄ (80 – x) P₂O₅– xEr₂O₃ with 0.1 $\le$x $\le$ 0.9 mol.% were prepared and assessed. X-ray diffraction (XRD) techniques were used to confirm the amorphous nature of the said samples. The structural units of phosphate-based glass were assessed from Raman spectra as ultra-(Q³), meta-(Q²), pyro-(Q¹) and orthophosphate (Q⁰) units. Depolymerization process of the glasses was testified for higher calcium oxide content and UV-visible for optical measurement. Thermal analysis have been investigated by means of thermogravimetric analysis. The results show the decomposition of materials in the temperature range of 25${}^{\circ }$C–1000${}^{\circ }$C. Er${}^{3+}$ absorption spectra were measured in the range of 400–1800nm. PL measurement was carried out in order to obtain the excitation and emission spectra of the samples. The emission spectra excited at 779nm comprises of 518nm, 550nm and 649nm of transition ⁴F${}_{9/2}$, ⁴S${}_{3/2}$ and ²H${}_{11/2}$ excited states to ⁴I${}_{15/2}$ ground state. In physical properties, the density calculated using Archimedes method is inversely proportional to molar volume with increase in Er${}^{3+}$ ions. Optical bandgap (E${}_g$) were determined using Tauc’s plots for direct transitions where E${}_g$ (direct) decreases with increase in erbium content. The refractive index increases with decreasing molar volume; this may have a tendency for larger optical bandgap. The result obtained from the glass matrix indicates that erbium oxide-doped calcium sulfate ultra-phosphate may give important information for wider development of functional glasses.

The glass-forming ability (GFA) and magnetic properties of the minor Zr-substituted Gd${}_{50}$Co${}_{50}$ amorphous alloy were investigated. The Gd${}_{50}$Co${}_{48}$Zr₂ amorphous ribbons prepared by melt-spinning show better GFA. With increasing minor Zr addition, the Gd${}_{50}$Co${}_{48}$Zr₂ amorphous ribbons possessed higher magnetic entropy change peak ($-\mathrm{\Delta }$S${}_m^{\mathrm{\text{peak}}}$ = 3.9 Jkg${}^{-1}$K${}^{-1}$, under 5 T) but lower Curie temperature (T${}_c$ = 231 K) than the Gd${}_{50}$Co${}_{50}$ amorphous alloy. The mechanism for the improved GFA, magnetocaloric effect (MCE) and the decrease in T${}_c$ was investigated. Finally, combined with other Gd-based amorphous ribbons, the Gd${}_{50}$Co${}_{48}$Zr₂ amorphous alloy was employed to construct amorphous composites to achieve a table-like magnetic entropy change profile, which can provide optimal efficiency when utilizing an Ericsson thermodynamic cycle.

As a pattern of cross-frequency coupling (CFC), phase–amplitude coupling (PAC) depicts the interaction between the phase and amplitude of distinct frequency bands from the same signal, and has been proved to be closely related to the brain’s cognitive and memory activities. This work utilized PAC and support vector machine (SVM) classifier to identify the epileptic seizures from electroencephalogram (EEG) data. The entropy-based modulation index (MI) matrixes are used to express the strength of PAC, from which we extracted features as the input for classifier. Based on the Bonn database, which contains five datasets of EEG segments obtained from healthy volunteers and epileptic subjects, a 100% classification accuracy is achieved for identifying seizure ictal from healthy data, and an accuracy of 97.67% is reached in the classification of ictal EEG signals from inter-ictal EEGs. Based on the CHB–MIT database which is a group of continuously recorded epileptic EEGs by scalp electrodes, a 97.50% classification accuracy is obtained and a raising sign of MI value is found at 6s before seizure onset. The classification performance in this work is effective, and PAC can be considered as a useful tool for detecting and predicting the epileptic seizures and providing reference for clinical diagnosis.

The Cu${}_{2-x}$Hg${}_x$Se (x = 0, 0.05, 0.10 and 0.15) nanopowders were fabricated using the hydrothermal synthesis, and then hot-pressed into bulk alloys. The effects of Hg doping on the thermoelectric (TE) properties of Cu₂Se were investigated. The electrical resistivities of all the doped samples are lower than that of the nondoped sample due to the induced cation vacancies. For the x = 0.10 and x = 0.15 samples, Seebeck coefficients increase slightly compared with the nondoped sample at higher temperature. Except for the sample of x = 0.05, the thermal conductivities of x = 0.10 and x = 0.15 samples are substantially lower than that of the x = 0.00 sample. As an overall result, the maximum value of ZT, which is the dimensionless TE figure of merit, reaches 1.50 at 600${}^{\circ }$C for the x = 0.10 sample.

We consider the single photon transistor in coupled cavity system of resonators interacting with multilevel superconducting artificial atom simultaneously. Effective single mode transformation is used for the diagonalization of the Hamiltonian and impedance matching in terms of the normal modes. Storage and transmission of the incident field are described by the interactions between the cavities controlling the atomic transitions of lowest lying states. Rabi splitting of vacuum-induced multiphoton transitions is considered in input/output relations by the quadrature operators in the absence of the input field. Second-order coherence functions are employed to investigate the photon blockade and delocalization–localization transitions of cavity fields. Spontaneous virtual photon conversion into real photons is investigated in localized and oscillating regimes. Reflection and transmission of cavity output fields are investigated in the presence of the multilevel transitions. Accumulation and firing of the reflected and transmitted fields are used to investigate the synchronization of the bunching spike train of transmitted field and population imbalance of cavity fields. In the presence of single photon gate field, gain enhancement is explained for transmitted regime.

Herein, a corrected theoretical model is proposed for modeling the static and dynamic behavior of electrostatically actuated narrow-width nanotweezers considering the correction due to finite dimensions, size dependency and surface energy. The Gurtin–Murdoch surface elasticity in conjunction with the modified couple stress theory is employed to consider the coupling effect of surface stresses and size phenomenon. In addition, the model accounts for the external force corrections by incorporating the impact of narrow width on the distribution of Casimir attraction, van der Waals (vdW) force and the fringing field effect. The proposed model is beneficial for the precise modeling of the narrow nanotweezers in nano-scale.

In this paper, knot physics on entangled vortex-membranes are studied including classification, knot dynamics and effective theory. The physics objects in this paper are entangled vortex-membranes that are called composite knot-crystals. Under projection, a composite knot-crystal is reduced to coupled zero-lattices. In the continuum limit, the effective theories of coupled zero-lattices become quantum field theories. After considering the topological interplay between knots and different types of zero-lattices, gauge interactions emerge. Based on a particular composite knot-crystal (we call it a standard knot-crystal), the derived effective model becomes the Standard Model. As a result, the knot physics may provide an alternative interpretation on quantum field theory.

We present a model to study the effects from external magnetic field, chemical potential and finite size on the phase structures of a massive four- and six-fermion interacting systems. These effects are introduced by a method of compactification of coordinates, a generalization of the standard Matsubara prescription. Through the compactification of the z-coordinate and of imaginary time, we describe a heated system with the shape of a film of thickness L, at temperature ${\beta }^{-1}$ undergoing first- or second-order phase transition. We have found a strong dependence of the temperature transition on the coupling constants $\lambda$ and $\eta$. Besides inverse magnetic catalysis and symmetry breaking for both kinds of transition, we have found an inverse symmetry breaking phenomenon with respect to first-order phase transition.

Barium chalcogenides are known for their high-technological importance and great scientific interest. Detailed studies of their elastic, mechanical, dynamical and thermodynamic properties were carried out using density functional theory and plane-wave pseudo potential method within the generalized gradient approximation. The optimized lattice constants were in good agreement when compared with experimental data. The independent elastic constants, calculated from a linear fit of the computed stress–strain function, were used to determine the Young’s modulus (E), bulk modulus (B), shear modulus (G), Poisson’s ratio ($\sigma$) and Zener’s anisotropy factor (A). Also, the Debye temperature and sound velocities for barium chalcogenides were estimated from the three independent elastic constants. The calculations of phonon dispersion showed that there are no negative frequencies throughout the Brillouin zone. Hence barium chalcogenides have dynamically stable NaCl-type crystal structure. Finally, their thermodynamic properties were calculated in the temperature range of 0–1000 K and their constant-volume specific heat capacities at room-temperature were reported.

Recently we studied the effect of photon addition in the initial coherent field on the entanglement swapping which causes some improvements in the process [Soltani et al., Int. J. Mod. Phys. B 31, 1750198 (2017)]. In this paper, we investigate the influence of multiphoton transitions in the atom–field interaction based on the cavity quantum electrodynamics on the entanglement swapping and show its considerable constructive effect on this process. The presented model consists of two two-level atoms namely A₁ and A₂ and two distinct cavity fields F₁ and F₂. Initially, the atoms are prepared in a maximally entangled state and the fields in the cavities are prepared in hybrid entangled state of number and coherent states, separately. Making the atom A₂ to interact with the field F₁ (via the generalized Jaynes–Cummings model which allows m-photon transitions between atomic levels in the emission and absorption processes) followed by their detection allows us to arrive at the entanglement swapping from the two atoms A₁, A₂ and the two fields F₁, F₂ to the atom–field A₁–F₂ system. Then, we pay our attention to the time evolution of success probability of detecting processes and fidelity. Also, to determine the amount of entanglement of the generated entangled state in the swapping process, the linear entropy is evaluated and the effect of parameter $m$ concerning the multiphoton transitions on these quantities is investigated, numerically. It is observed that, by increasing the number of photons in the transition process, one may obtain considerable improvement in the relevant quantities of the entanglement swapping. In detail, the satisfactorily acceptable values 1 and 0.5 corresponding to success probability and fidelity are obtained for most of the times during observing of the above-mentioned procedure. We concluded that the presented formalism in this paper is much more advantageous than our presentation model in our earlier work mentioned above.

We study conceptional problems of a photo-electron emission (PEE) process from a free exciton in insulating crystals. In this PEE process, only the electron constituting the exciton is suddenly emitted out of the crystal, while the hole constituting the exciton is still left inside and forced to be recoiled back to its original valence band. This recoil on the hole is surely reflected in the spectrum of the PEE with a statistical distribution along the momentum–energy curve of the valence band. This distribution is nothing but the square of the exciton wavefunction amplitude, since it shows how the electron and the hole are originally bound together. Thus, the momentum-resolved PEE can directly determine the exciton wavefunction. These problems are clarified, taking the $\mathrm{\Gamma }$ and the saddle point excitons in GaAs, as typical examples. New PEE experiments are also suggested.

The glass samples were prepared in accordance with the formula: (30-x)SrO–xAl₂O₃–69.8B₂O₃–0.2Cr₂O₃ (0 $\le$x $\le$ 15 mol %) by melt quenching method. The absence of Bragg’s peaks confirmed the amorphous nature of the prepared glass samples. It was observed that the molar volume was increasing while the density is decreasing with increasing of Al₂O₃ content. Optical absorption study was performed to evaluate the optical bandgap, oxygen packing density, ionic packing density and Urbach energies. The Racah parameters (B and C) and D${}_q$/B ratio have been calculated. Fourier transform infrared (FTIR) spectra recorded in the region from 400–1600 cm${}^{-1}$ at room-temperature (RT) confirmed the formation of BO₃, BO₄ and AlO₄ groups upon the addition of strontium oxide as modifier. The Raman spectra of all the glasses recorded over continuous spectral range 200–1600 cm${}^{-1}$ exhibited different spectral bands. The EPR spectra recorded at 9.7 GHz (X-band frequency) have four resonance signals. The signal at g $\approx$ 5.33 is due to Cr${}^{3+}$ ion sites of rhombic symmetry and signal at g $\approx$ 1.97 is due to contribution from Cr${}^{3+}$ and Cr${}^{5+}$ ion pairs.

Ferroelectric Pb(ZrTi)O₃ (PZT) nanotubes were prepared by sol–gel method and porous anodic alumina (PAA) membrane using spin-coating technique. This method is based on filling-pyrolysis-filling process and the use of one-stage alumina membranes. One of the advantages of this method is its rapidity, which takes only 1 h time before the calcination step. The effect of repeated pores filling was investigated to get the required size of nanotubes. The field emission scanning electron microscope (FE-SEM) images were shown that the PZT nanotubes have inner diameters in the range of 65–90 nm and length of about 50–60 $\mu$m. This means that the samples have a significant aspect ratio (700–800). Also the FE-SEM image confirmed that the highly ordered, hexagonally distributed PAA membranes with the pore diameter about 140–150 nm were formed. The X-ray diffraction (XRD) results showed that the PZT nanotubes have a tetragonal structure. The metal oxide bands like ZrO₆ and TiO₆ of the final PZT nanotubes were detected by Fourier transform infrared (FT-IR) analysis and confirmed the formation of perovskite structure. By using FT-IR spectroscopy and Kramers–Kronig transformation method, the optical constants like real ${𝜀}_1$($\omega$) and imaginary ${𝜀}_2$($\omega$) parts of dielectric function, extinction coefficient k($\omega$) and refractive index n($\omega$) were determined. It was shown that the optical constants of PZT nanotubes are different from PZT nanoparticles.