International Journal of Modern Physics B

Having accepted a more generalized form for density-displacement type electron–phonon interaction (EPI) force we studied the simultaneous effect of uniaxial strains and EPI’s screening on the temperature of Bose–Einstein condensation $(T_{\mathrm{\text{BEC}}})$ of the ideal gas of intersite bipolarons. $T_{\mathrm{\text{BEC}}}$ of the ideal gas of intersite bipolarons is calculated as a function of both strain and screening radius for a one-dimensional chain model of cuprates within the framework of Extended Holstein–Hubbard model. It is shown that the chain model lattice comprises the essential features of cuprates regarding of strain and screening effects on transition temperature $(T_c)$ of superconductivity. The obtained values of strain derivatives of $\partial T_{\mathrm{\text{BEC}}}/\partial {𝜀}_i$ $(i=a,c)$ are in qualitative agreement with the experimental values of $\partial T_c/\partial {𝜀}_i$ $(i=a,b,c)$ of La${}_{2-x}$Sr${}_x$CuO₄ under moderate screening regimes.

In this paper, we investigate the possibility to use the Wigner function to detect and quantify quantum correlations in general. We study these quantum correlations for two quasi-Werner states formed with two general bipartite superposed squeezed states. We find then that the Wigner function is not sensitive to all kinds of quantum correlations but it only witnesses entanglement.

As is known, cuprate superconductors, which have intrinsic Josephson junctions, are used as terahertz sources. In this context, a great number of studies on the intensification of the plasma frequency in terahertz region are devoted to the fabrication of mesa structures in superconductors. It has been previously investigated by some researchers that the resonant state of cuprate superconductors enhances the power of the plasma frequency in terahertz range. As is known, the mercury-based superconductors exhibit three-dimensional Bose–Einstein condensations; hence the resonant state occurs in the sample. From this point of view, mesa structures, which are intrinsically formed in mercury cuprates, have been investigated to enhance the plasma frequency in this work. Also, I have found a physical relation between the lateral size and the Josephson penetration depth of the superconducting sample. Moreover, it has been found that at upper and the lateral size values with microdimension, the superconductors investigated behaves as a bulk in the context of the critical parameters. Furthermore, the method recommended in this study would make crucial contributions to technological applications on mesa structures in order to determine the convenient mesa size that prevents vesting time and energy for the fabrication.

A quantum particle subjected to a constant force undergoes an accelerated motion following a parabolic path, which differs from the classical motion just because of wave packet spreading (quantum diffusion). However, when a periodic potential is added (such as in a crystal) the particle undergoes Bragg scattering and an oscillatory (rather than accelerated) motion is found, corresponding to the famous Bloch oscillations (BOs). Here, we introduce an exactly-solvable quantum Hamiltonian model, corresponding to a generalized Wannier–Stark Hamiltonian $Ĥ$, in which a quantum particle shows an intermediate dynamical behavior, namely an oscillatory motion superimposed to an accelerated one. Such a novel dynamical behavior is referred to as accelerated BOs. Analytical expressions of the spectrum, improper eigenfunctions and propagator of the generalized Wannier–Stark Hamiltonian $Ĥ$ are derived. Finally, it is shown that acceleration and quantum diffusion in the generalized Wannier–Stark Hamiltonian are prevented for Airy wave packets, which undergo a periodic breathing dynamics that can be referred to as Airy–Bloch oscillations.

The relativistic theory of the Dirac fermions moving on cylinders in external Aharonov–Bohm (AB) field is built starting with a suitably restricted Dirac equation whose spin degrees of freedom are not affected. The exact solutions of this equation on finite or infinite AB cylinders allow one to derive the relativistic circular and longitudinal currents pointing out their principal features. It is shown that all the circular currents are related to the energy in the same manner on cylinders or rings either in the relativistic approach or in the nonrelativistic one. The specific relativistic effect is the saturation of the circular currents for high values of the total angular momentum. Based on this property some approximative closed formulas are deduced for the total persistent current at $T=0$ on finite AB cylinders. Moreover, it is shown that all the persistent currents on finite cylinders or rings have similar nonrelativistic limits.

Detailed first-principle calculations of properties in zinc blende quaternary alloy ${\mathrm{\text{B}}}_x{\mathrm{\text{Al}}}_y{\mathrm{\text{In}}}_{1-x-y}\mathrm{\text{N}}$ at various concentrations are investigated using density functional theory (DFT) within virtual crystal approximation (VCA) implemented in alchemical mixing approximation. The calculated bandgaps show direct transitions at $\mathrm{\Gamma }$–$\mathrm{\Gamma }$ and indirect transitions at $\mathrm{\Gamma }$–$X$, which are opened by increasing boron concentration. The density of state (DOS) revealed upper valence band (VB1) domination by $p$-states atoms, while $s$-states dominate the lower valence band (VB2); also, the DOS shows the contribution of $d$-states to the conduction band. The first critical point in the dielectric constant ranges between 0.07–4.47 eV and is due to the first threshold optical transitions in the energy bandgap. Calculated static dielectric function (DF) ${𝜖}_1(0)$ is between 5.15 and 10.35, an indication that small energy bandgaps yield large static DFs. The present results indicate $\mathrm{\text{ZB}}$-${\mathrm{\text{B}}}_x{\mathrm{\text{Al}}}_y{\mathrm{\text{In}}}_{1-x-y}\mathrm{\text{N}}$ alloys are suitable candidates of deep ultraviolet light emitting diodes (LEDs), laser diodes (LDs) and modern solar cell since the concentrations $x$ and $y$ make the bandgap and lattice constant of $\mathrm{\text{ZB}}$-${\mathrm{\text{B}}}_x{\mathrm{\text{Al}}}_y{\mathrm{\text{In}}}_{1-x-y}\mathrm{\text{N}}$ quaternary alloys tunable to desirable values.

Magnetic hysteresis behavior of isotropic permalloy elliptic nanorings of outer semi-major axis length $(a_{\mathrm{\text{out}}})$ 100 nm and thickness $(t)$ 20 nm were studied with respect to the variation of two parameters: outer semiminor axis length $(b_{\mathrm{\text{out}}})$ and the difference between outer and inner dimensions $(r)$. The outer semiminor axis length $(b_{\mathrm{\text{out}}})$ varied from 90 nm to 20 nm which covers from nearly circular nanoring to elliptic nanoring of high aspect ratio. The value of $r$ varied in steps of 10 nm. Micromagnetic simulation of in-plane hysteresis curve of these nanorings revealed that the remanent state of all of these elliptic rings are onion states if the magnetic field is applied along the longer side of the elliptic rings. If the magnetic field is applied along the shorter side, then the remanent states turn out to be vortex state. The hysteresis loss indicated by area of the hysteresis loop was found to be decreasing gradually with the increment of either $r$ or $b_{\mathrm{\text{out}}}$. On the other hand, the remanent magnetization increased with increment of $r$ but decreased with the increment of $b_{\mathrm{\text{out}}}$. The changes were attributed to three parameters mainly: inner curvature, exchange energy and demagnetization energy. The changes in loop area were discussed in light of variation of these three parameters.

On the basis of the Rytov approximation, we investigate the effects of non-Kolmogorov turbulence on the spread of the spiral spectrum and the received power of multi-modified Bessel–Gaussian Schell (MMBGS) beams carrying orbital angular momentum. Numerical results show that the spread of the spiral spectrum increases as the azimuthal index of the source increases and that an optimal value of the beam waist is obtained. We find that the spread of partially coherent MMBGS beams with short wavelength is more robust than that of beams with long wavelength. The complete reverse is true for fully coherent MMBGS beams.

We have investigated the thermal conductivity of defective fullerene (C${}_{60})$ by using the nonequilibrium molecular dynamics (MD) method. It is found that the thermal conductivity of C${}_{60}$ with one defect is lower than the thermal conductivity of perfect C${}_{60}$. However, double defects in C${}_{60}$ have either positive or negative influence on the thermal conductivity, which depends on the positions of the defects. The phonon spectra of perfect and defective C${}_{60}$ are also provided to give corresponding supports. Our results can be extended to long C${}_{60}$ chains, which is helpful for the thermal management of C${}_{60}$.

The dynamical stability and its connection with phase structures of binary Bose–Einstein condensates (BECs) are systematically studied within framework of the Gross–Pitaevskii (GP) theory. We find that (a) the dynamical stability is the main factor governing both the symmetry breaking and the formation of various phases associated with the scenarios: symmetry restoration (SR) and inverse symmetry breaking (ISB); (b) the condensation of Bose gases might occur at constant temperature for chemical potentials varying in some definite regions. We suggest how to experimentally observe the foregoing phenomena whose possible existences in nature are theoretically confirmed.

Within the framework of effective mass approximation, the scattering rate via longitudinal optical (LO) phonon emission for an electron and the mean scattering rate via LO phonons emission for electrons initially in the first excited sub-band and finally in the ground sub-band in ${\mathrm{\text{Ga}}}_x{\mathrm{\text{In}}}_{1-x}{\mathrm{\text{As}}}_y{\mathrm{\text{P}}}_{1-y}/\mathrm{\text{InP}}$ stepped quantum well (QW) is calculated adopting the shooting method and Fermi’s golden rule. The results show that the scattering rate and the mean scattering rate are highly dependent on alloy compositions, well width, initial electron energy, electron temperature and sub-band separation $E_{21}$ between the ground sub-band and the first excited sub-band. When $E_{21}$ is larger than the LO phonon energy, the scattering rate and the mean scattering rate increases with increasing Ga composition, decreasing As composition and increasing well width. However, when $E_{21}$ is smaller than the LO phonon energy, its change tendency is contrary. The scattering rate increases with decreasing initial electron energy if the separation between the initial electron energy and the ground state energy $E_1$ is not smaller than the LO phonon energy. The scattering rate and the mean scattering rate increases with rising electron temperature. The mean scattering rate reaches the maximum value when $E_{21}$ is equal to the LO phonon energy. The interruption in the scattering rate happens when the separation between the initial electron energy and $E_1$ is smaller than the LO phonon energy. The rapid decrease of the mean scattering rate happens when $E_{21}$ is smaller than the LO phonon energy if $E_{21}$ continues decreasing. In addition, both the scattering rate and the mean scattering rate show little change with different stepped layer widths.

In this article, we use population balance based dynamic friction model for steady sliding to develop scaling laws in the terms of mesh size of gelatin hydrogels. First of all, it is observed in the sliding experiments that shear modulus of gelatin hydrogels depends on sliding velocity. This dependence is more evident in the case of low sliding velocity. Moreover, relaxation time constant of a dangling chain at the sliding interface scales with the same exponent as its stiffness. The scaling law is also developed for chain density and viscous retardation at the sliding interface. It is also established that the Hookean-based dynamic friction model is sufficient to study frictional behaviour of hydrogels. The reason for this observation is attributed to the weak bonding between a gelatin hydrogel and glass interface.