International Journal of Modern Physics B

The electronic and optical properties of pentagonal B₂C (penta-B₂C) monolayer are investigated by means of the first-principles calculations in the framework of the density functional theory. The cohesive energy consideration confirms the good stability of the B₂C nanostructure in this phase. The electronic band structure reveals that the valence band maximum (VBM) is located at $X$-point of the first Brillouin zone (BZ) whereas the conduction band minimum (CBM) is situated at the center of the BZ, resulting in an indirect energy bandgap of about 1.5 eV. Furthermore, a calculated low absorption and low reflection of the material in low energy ranges denote the transparency of the B₂C monolayer in the investigated range for normal light incidence. The obtained results may find application in fabrication of future opto-electronic devices.

Starting from the Holstein model, we have investigated the effects of Rashba spin–orbit coupling (RSOC) on density of states (DOS), electronic heat capacity (EHC) and magnetic susceptibility (MS) of boron nitride-doped (BN-doped) graphene beyond the Dirac cone approximation within the Green’s function approach. By using the self-consistent perturbation theory, retarded self-energy can be calculated. We have found that the band gap (the peak of EHC and MS) of the system increases (decreases) with RSOC and electron–phonon (e–ph) interaction. Also, the Schottky anomaly moves only to the higher temperatures for strong RSOCs and e–ph interactions. Also, our results show that the response of the system to an external magnetic field is scaled down in the presence of RSOC and e–ph interaction.

Correlations in open quantum systems exhibit peculiar phenomena under the effect of various sources of noise. Here, we investigate the dynamics of entanglement and quantum discord (QD) for three noninteracting qubits coupled with a classical environmental static noise characterized by an external random field. Two initial entangled states of the system are examined, namely, the GHZ- and $W$-type states. The system-environment interaction is here analyzed in three different configurations, namely, independent, mixed and common environments. We find that the dynamics of quantum correlations are strongly affected by the type of system-environment interaction and the purity of the initial entangled state. Indeed, depending on the type of interaction and the value of the purity of the initial state, peculiar phenomena such as sudden death, revivals and long-time survival of quantum correlations are observed. On the other hand, our results clearly show that quantum correlations initially present in the $W$-type states are less robust than those of the GHZ-type states. Furthermore, we find that the long-time survival of entanglement can be detected by means of the suitable entanglement witnesses.

This work presents salient features of a new photonic crystal fiber composed of silica in background and coating of gold in holes. This has been done by computing the effective refractive index of semi-vectorial wave propagation equation using the dielectric properties of these materials by finite difference method under analytical boundary condition. The effect of the different filling factor of gold and also the effect of intensity on wave propagation are analyzed respectively with the same adequate physical condition. These results should be useful in obtaining the flattened dispersion with a small effective area in the presence of nonlinearity.

Based on the order flow data of a stock and its warrant, the immediate price impacts of market orders are estimated by two competitive models, the power-law model (PL model) and the logarithmic model (LG model). We find that the PL model is overwhelmingly superior to the LG model, regarding the robustness of the estimated parameters and the accuracy of out-of-sample forecasting. We also find that the price impacts of ask and bid orders are consistent with each other for filled trades, since significant positive correlations are observed between the model parameters of both types of orders. Our findings may provide valuable insights for optimal trade execution.

Membrane-type acoustic metamaterials (MAMs) with negative dynamic mass have demonstrated the effects in the sound transmission loss (STL) at low-frequency range. This research aims to design a membrane-type acoustic metamaterial muffler (MAMM) based on the present MAMs, and to solve the problem that airflow cannot flow unimpededly in the channel once using the MAMs. For a better understanding of MAMM, the resonance frequency of the membrane was calculated and simulation was used to study the acoustic transmission performance of the MAMM. The simulation results were verified in comparison with the theoretical results of the membrane. This MAMM reduced the structural size of muffler compared with the traditional Helmholtz muffler and expand muffler, which can find application for the MAMs in acoustic absorption and noise control.

Binding energies of the heavy hole and light hole exciton in a quantum well with Pöschl–Teller (PT) potential composed of GaAs have been studied variationally within effective mass approximation. The effects of pressure and temperature on exciton binding energy are analyzed individually and also simultaneously for symmetric and asymmetric configuration of the well. The results show that exciton binding energy (i) decreases as the well width increases, (ii) increases with pressure and (iii) decreases with temperature. Simultaneous effects of these perturbations lead to more binding of the exciton. The results are compared with the existing literature.

Effects of vacancy on the microstructural and magnetic properties in self-doped La${}_{1-x}$MnO${}_{3+\delta }$ $(x\le 0.3)$ manganites have been studied. The samples crystallize in a single phase of rhombohedral structure exhibiting R$\bar{3}$C space group until $x$-value reaches 0.2. As self-doped concentration increases, structural distortion is confirmed by combining X-ray diffraction. Ferromagnetic (FM) and antiferromagnetic (AFM) coupling is found and exchange bias effect appears at low temperature. Ferromagnetic diffuse phase transition (FDPT) is induced by Griffiths phase for $x\ge 0.1$ at temperature of $T>T_C$. The FM transition temperature range is increased from 32 K to 150 K. The enhancement of Griffiths phase with $x$ for $x\ge 0.1$ is explained by the greater $A$-site spatial disorder and the structural distortion.

We analyze the effects of quantum correlations on the parameter precision in an interferometric configuration. As probe states, we consider a class of two-qubit states for which the analytical expression of the quantum interferometric power, quantifying the quantum correlations, is explicitly derived. Also, we give and analyze the local quantum Fisher information, which evaluates the sensitivity of the probe state to the phase shift, for some relevant local Hamiltonians. The discord-like quantum correlations based on the notion of quantum interferometric power are compared with the original quantum discord based on von Neumann entropy. We also examine the significance of quantum correlations in enhancing the precision of the phase estimation. Our study corroborates the recent series of investigations focusing on the role of quantum correlations other than entanglement on the efficiency of quantum metrology protocols.

In this paper, the effect of dilute charged impurity and external magnetic field on orbital-resolved density of states (DOS) and electronic heat capacity (EHC) of a monolayer hydrogenated graphene which is called chair-like graphane is investigated within the Harrison model and Green’s function technique. The self-consistent Born approximation has been implemented to describe the effect of scattering between electrons and dilute charged impurities. Our results show that the graphane is a semiconductor and its band gap decreases with impurity and magnetic field. EHC reaches almost linearly to Schottky anomaly and does not change at low temperatures in the presence of impurity and magnetic field. Generally, EHC increases with the mentioned parameters. Surprisingly, impurity doping only affects the salient behavior of $p_y$ orbital contribution of carbon atoms due to the symmetry breaking.

Mechanical and electronic properties of oxygen plasma-treated graphene sheets are investigated using density functional theory (DFT). Oxygen plasma-treated graphene is modeled using a graphene sheet with adsorbed epoxide functional groups (C–O–C) on its one side. The most stable configurations of such oxidized graphene sheets with different O/C ratios ranging from 12.5% to 50% are then calculated. In the special case of O/C = 50% (fully oxidized surface), both single- and double-sided oxidation cases are considered. The elastic and electronic properties of the energetically most favorable configurations are evaluated under the tensile and compressive loads in harmonic range. For structures with high O/C ratios (O/C $\ge$ 25%), the elastic constants (modulus of elasticity and bulk modulus) are significantly smaller than those of graphene while for low O/C ratios (O/C $\le$ 12.5%), these quantities are almost equal to the elastic constants of pristine graphene. We also found that the electronic bandgap of the oxidized sheets is increased under tensile loading.

In the present paper, the optical properties of a GaAs wedge-shaped quantum dot (QD) under the effect of Rashba spin–orbit interaction (SOI) are theoretically studied. For this purpose, we have used analytical expressions for optical properties obtained by the compact-density matrix formalism. The dependence of the optical absorption coefficients and refractive index changes on the strength of Rashba SOI for different angles and different radii of wedge-shaped QD has been studied. According to the obtained results, it is found that (i) the Rashba SOI does not have considerable effects on the refractive index changes maxima. (ii) The total absorption coefficient is increased and shifted towards higher energies with considering the Rashba SOI. (iii) The influence of Rashba SOI on the optical properties depends on the parameters such as apex angle and radius of the wedge-shaped QD.