International Journal of Modern Physics B

Fluorinated graphene was irradiated by electron beam, and the changing of fluorinated graphene after electron beam irradiation was found by several detection techniques of Raman, electrical characterization and X-ray photoelectron spectroscopy (XPS). Raman spectra and electric characterization confirmed that the crystal structure and electrical performance of graphene was recovered partially after electron beam irradiation. XPS results indicated that the concentration of fluorine quickly dropped from 35% to 15% just after 30 min irradiation, and then dropped, slowly to 10% with the irradiation time to 150 min. The results indicate that stimulate fluorine desorption from fluorinated graphene used electron beam completely is difficult, which means a big challenge for ESD to fabricate all graphene electronics.

The carrier effective masses as well as thermoelectric and electronic properties of ternary chalcogenides compounds of the form Ag₃AuX₂(X = Se, Te) have been studied using first-principles method based on density functional theory. For the treatment of exchange-correlation energy, we have used the generalized gradient approximation (GGA) by Perdew, Burke and Ernzerhof (PBE-GGA) and Wu–Cohen (WU-GGA) schemes. Both the compounds (Ag₃AuSe₂ and Ag₃AuTe₂) are direct bandgap semiconductors. The p-type nature of these compounds is confirmed by the effective mass calculations. In thermoelectric measurements, different parameters (electrical conductivity, carrier concentration, Seebeck coefficient, thermal conductivity and thermoelectric power) are calculated. It is found that all these parameters increase with the increase in temperature for both the compounds. The obtained results for these compounds such as the direct bandgap nature and their high value of the thermoelectric power make them valuable candidates for different device applications.

We have investigated the phonon, mechanical and thermodynamic properties of B2-phase AlY under high pressure by performing density functional theory (DFT). The result of phonon band structure shows B2-phase AlY exhibits dynamical stability. Then, the elastic properties of AlY under high pressure have been discussed. The elastic constants of AlY increase monotonically with the increase of the pressure and all the elastic constants meet the mechanical stability standard under high pressure. By analyzing the Poisson’s ratio $\nu$ and the value of B/G of AlY, we first predicted that AlY undergoes transformation from brittleness to ductility at 30 GPa and high pressure can improve the ductility. To obtain the thermodynamic properties of B2-phase AlY, the quasi-harmonic Debye model has been employed. Debye temperature ${\mathrm{\Theta }}_D$, thermal expansion coefficient $\alpha$, heat capacity C${}_p$ and Grüneisen parameter $\gamma$ of B2-phase AlY are systematically explored at pressure of 0–75 GPa and temperature of 0–700 K.

We analyze the evolution of an entangled many-body state in a Josephson tunneling junction and its dependence on the number of bosons and interaction strength. A N00N state, which is a superposition of two complementary Fock states, appears in the evolution with sufficient probability only for a moderate many-body interaction on an intermediate time scale. This time scale is inversely proportional to the tunneling rate. Many-body interaction strongly supports entanglement: The probability for creating an entangled state decays exponentially with the number of particles without many-body interaction, whereas it decays only like the inverse square root of the number of particles in the presence of many-body interaction.

By using the extended Hubbard model under the Hartree–Fock approximation, we theoretically investigate the effect of electron–electron interaction on the polarization of the single-photon excited state of the charged $\pi$-conjugated oligomer. In the framework of one-dimensional tight-binding model, a uniform weak electric field is applied for polarization. The results show that the polarization property will vary with the electron–electron interaction. For example, with the increase of on-site Coulomb interaction strength, the value of the induced dipole moment is decreased. Its physical origin is revealed by analyzing the wavefunction of the localized energy level. In addition, the relation between the critical electric field for the dissociation of the single-photon excited state of the charged oligomer and the electron–electron interaction strength is also discussed.

Graphene has brought forward a lot of new physics. One of them is the emergence of massless Dirac fermions in addition to the electrons and these features are new to physics. In this theoretical study, the signatures for quantum scar and the breakdown of universality in graphene are investigated with reference to the presence of these two types of fermions. Taking the graphene quantum dot (QD) potential as the confining potential, the radial part of Dirac equations are solved numerically. Concentrations of the two component eigen-wavefunctions about classical periodic orbits emerge as the signatures for the quantum scar. The sudden variations, in the ratio of the radial wave-functions (large and small components), R(g/f), with mass ratio $\kappa$ are the signatures for breakdown of universality in graphene. The breakdown of universality occurs for the states k = −1 and k = 1, and the state k = −1 is more susceptible to the breakdown of universality.

The effect of roughness and correlation on the Casimir torque is studied. The plates are assumed to be perfect conductors. This is a good approximation when the separation between plates is not too small. The pairwise summation (PWS) method is used, which is a good approximation when the correlation length is much larger than the distance between the plates. Torque components both parallel and perpendicular to the plates are obtained. It is seen that the component parallel to the plates is nonvanishing even if the plates are smooth, but there are contributions due to roughness and correlation as well, and the contribution of the correlation is an increasing function of both the roughness exponent and the correlation length. The component perpendicular to the plates, however, is nonvanishing only if the plates are rough and correlated to each other. As the roughness exponent increases, this component increases, reaches a peak and then decreases.

Transport of an inertial Brownian particle driven by the multiplicative Lévy noise was investigated here. Numerical results indicate that: (i) The Lévy noise is able to induce absolute negative mobility (ANM) in the system, while disappearing in the deterministic case; (ii) the ANM can occur in the region of superdiffusion while disappearing in the region of normal diffusion, and the appropriate stable index of the Lévy noise makes the particle move along the opposite direction of the bias force to the maximum degree; (iii) symmetry breaking of the Lévy noise also causes the ANM effect. In addition, the intrinsic physical mechanism and conditions for the ANM to occur are discussed in detail. Our results have the implication that the Lévy noise plays an important role in the occurrence of the ANM phenomenon.

In this paper, the ferroelectric transition and dielectric properties of the lead monohydrogen phosphate (PbHPO₄) crystal are theoretically investigated. By using Green’s function method and modified two sublattice pseudospin–lattice coupled mode model, formulae for PbHPO₄ type crystals are derived. Temperature variations of ferroelectric mode frequency, dielectric constant and loss tangent are calculated for the PbHPO₄ crystal. Our results agree well with the experimental data.

Optical and electronic properties of ZB, RS and WZ structures of gallium nitride (GaN) are studied in equilibrium and under pressure using the first-principles calculation in the density functional theory (DFT) framework to obtain quantities like dielectric function, loss function, reflectance and absorption spectra, refractive index and their relation parameters. The electronic properties are studied using EV-GGA and GGA approximations and the results calculated by EV-GGA approximation were found to be much closer to the experimental results. The interband electron transitions are studied using the band structure and electron transition peaks in the imaginary part of the dielectric function; these transitions occur in three structures from N-2p orbital to Ga-4s and Ga-4p orbitals in the conduction band. Different optical properties of WZ structure were calculated in two polarization directions of (100) and (001) and the results were close to each other. Plasmon energy corresponding to the main peak of the energy-loss function in RS with the value of 26 eV was the highest one, which increased under pressure. In general, RS shows more different properties than WZ and ZB.

The vibrational properties of double-walled carbon nanocones are investigated herein. The double-walled carbon nanocones with different geometries including apex angles and lengths are considered. The simply supported–simply supported, clamped-free and clamped–clamped boundary conditions are applied on the nanocones. A linear elastic beam-based finite element method is employed to obtain the frequencies of the double-walled carbon nanocones. Elastic beam elements are used to model the carbon–carbon bond in the structure of the nanocones. Besides, the spring elements are employed to describe the nonbonding van der Waals interactions between different layers. Natural frequencies and mode shapes of the double-walled carbon nanocones are extracted by solving the eigenvalue problem. It is observed that increasing the disclination angle of nanocones increases their natural frequency. However, increasing the nanocone’s height leads to decreasing the frequency.

Spin-polarized density functional calculations are performed to study the correlation and spin-orbit coupling (SOC) effects in scandium intermetallic compounds viz. ScTM (TM=Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au) using FP-LAPW+lo method. The LDA, LDA+U and LDA+U+SOC exchange-correlation functionals are used to calculate the structural parameters and we found that the LDA+U results are consistent with the experiments. The electronic properties reveal that these compounds are metallic in nature. Correlations effects are determined using the U/W ratio and we found that ScCo, ScIr, ScPd, ScPt, ScCu and ScAg are highly correlated compounds, whereas ScRh, ScNi and ScAu are intermediately correlated compounds. Furthermore, stable magnetic phase for each compound is optimized, which reveals that ScCo, ScRh, ScPd, ScPt and ScCu are stable in ferromagnetic phase, ScIr, ScNi and ScAu are anti-ferromagnetic, whereas ScAg is a nonmagnetic material.

In this paper, the phenomenon of stochastic resonance in FitzHugh–Nagumo (FHN) neural system driven by correlated non-Gaussian noise and Gaussian white noise is investigated. First, the analytical expression of the stationary probability distribution is derived by using the path integral approach and the unified colored noise approximation. Then, we obtain the expression of signal-to-noise ratio (SNR) by applying the theory of two-state model. The results show that the phenomena of stochastic resonance and multiple stochastic resonance appear in FHN neural system under different values of parameters. The effects of the multiplicative noise intensity D and the additive noise intensity Q on the SNR are entirely different. In addition, the discharge behavior of FHN neural system is restrained when the value of Q is smaller. But, it is conducive to enhance signal response of FHN neural system when the values of Q and D are relatively larger.

Exact and approximate master equations were derived by the projection operator method for the reduced statistical operator of a multi-level quantum system with finite number N of quantum eigenstates interacting with arbitrary external classical fields and dissipative environment simultaneously. It was shown that the structure of these equations can be simplified significantly if the free Hamiltonian driven dynamics of an arbitrary quantum multi-level system under the influence of the external driving fields as well as its Markovian and non-Markovian evolution, stipulated by the interaction with the environment, are described in terms of the SU(N) algebra representation. As a consequence, efficient numerical methods can be developed and employed to analyze these master equations for real problems in various fields of theoretical and applied physics. It was also shown that literally the same master equations hold not only for the reduced density operator but also for arbitrary nonequilibrium multi-time correlation functions as well under the only assumption that the system and the environment are uncorrelated at some initial moment of time. A calculational scheme was proposed to account for these lost correlations in a regular perturbative way, thus providing additional computable terms to the correspondent master equations for the correlation functions.