In this paper, the effect of magnon scattering, light–matter coupling strength, temperature, and applied dc field H0 on magnon dispersion, density of magnons, magnetization, and thermodynamic ...properties of 2D-Sc/GaAs DMS material is studied. The Green function formalism is used to find the magnon dispersion and density in single-mode excitation employing the quantum field theory. Our findings indicate that ferromagnetic phase change is obtained within a limited low-temperature range based on the product Ω0T5/2, which remains below unity and varies with the amount of magnon scattering factor Ω0. It was presumed that the density of localized magnetic impurities can be controlled by taking into account the numerical stability with the number of holes required for mediation, and therefore, a scandium (Sc) dopant and its kind, which have a double functionality of creating holes and adding magnetic impurities from their 3d suborbital, are the best choice to replace those with higher spin magnetic moments. We also observe that the magnetic curves broaden as the temperature further rises and decrease with the enhancement of the magnon scattering factor, perhaps, due to quenching of fermionic spins ceasing the interband excitation. However, in the absence of this factor, the magnetization decreases linearly with the increase in the temperature, breaking the Bloch T3/2 low, perhaps, introducing anomalous condition to such 2D materials. The light–matter coupling strength and the dc field H0 are alleged to be responsible for the formation of the energy gap and variation of magnon dispersion. This work suggests that there is a point above which the temperature TC may not rise with the increase in the impurity concentration x due to magnon scattering, distressing the entire thermodynamic property.
The interface between the active layer and the charge-transporting layer is critical for performance improvement in polymer solar cells (PSCs). The use of zinc oxide (ZnO) as an electron transport ...layer (ETL) in PSCs was limited due to inherent defects in the surface of ZnO prepared by the sol-gel method, mismatched energy bands with the photoactive layer, and incompatibility between the photoactive layer and ZnO ETL. In this study, nitrogen and phosphorus codoped carbon dots (N & P-CDs) were prepared from Ensete ventricosum (false banana) and used as an interfacial modification layer for ZnO ETL. The inverted devices with structures ITO/ZnO/N & P-CD/PTB7:PC70BM/Al were fabricated to investigate the charge transfer dynamic between the active layer and ETL interface modification with N & P-CDs. We have observed that the interfacial modification between the ZnO ETL and the active layer, using N & P-CDs, improves the charge transfer between ZnO ETL and PTB7:PC70BM active layer. The obtained result shows that the ETL/BHJ interface resistance of the devices with ZnO:undoped CDs, ZnO:N-CDs, ZnO:P-CDs, and ZnO:N & P-CD ETLs decreases dramatically from 103.4 to 84.04, 78.16, 37.88, and 28.9 Ω, respectively. This is due to the improvement of charge extraction efficiency by smoothing ZnO surface defects and minimizing the band mismatch between the active layer and ZnO using N & P-CDs. The results indicate that the water-soluble N & P-CDs developed in this study have the potential to be used for efficient free charge carrier extraction for PSCs.
This article investigates the dynamics of spin waves in two sublattice antiferromagnetic (AFM) system spins’ interaction and magnon dispersion relation. The analysis is done starting with a standard ...model that includes a uniaxial magnetic anisotropy field. Quantum field theory is employed in formulating the problem, and double-time temperature-dependent Green function technique is used to obtain magnon dispersion, whereby random phase approximation is considered to decouple and diagonalize the higher order terms. At low temperatures and long wavelength approximation, dispersion of uniaxial symmetric AFM crystal lattice of metallic fluoride materials, such as MnF2, FeF2, and RbMnF3, is analyzed for illustration. Our findings indicate that as the anisotropic field increases, the magnon dispersion vs wave vector k gradually varies, attempts linearity from being curved, and attains a sinusoidal structure when extended further in the first Brillouin zone. Perhaps, these results are useful to understand the feature of magnon dispersion of stable similar AFM materials for practical application.
Ternary boron-carbon-nitride compounds are the hardest, chemically stable, and most applicable semiconductors in optoelectronic devices. We investigate the quasi-particle and excitonic properties of ...type II o-BC2N using many-body perturbation theory (MBPT). The state-of-the-art GW and BSE methods were used to determine the accurate band gap and excited-state characteristics of this material. We simulate the convergence test and structural optimization in DFT, which is the starting point for the GW calculation. We also compute the convergence test of the parameters in GW and BSE. As a result, the bandgap of our system is found to be 2.31 eV and 1.95 eV using the GW approximation and DFT-PBE, respectively. Since the valence and conduction band edges are located at different Brillouin zones, we decide that o-BC2N is an indirect bandgap semiconductor. In addition, by applying the scissor operator, we corrected the quasi-particle bandgap, which shows almost the same result as the GW approximation. Furthermore, using the BSE algorithm, we calculate the optical bandgap of type II o-BC2N to be 4.0 eV with the excitonic effect and 4.4 eV without the excitonic effect. The highest peaks of the imaginary dielectric function with the excitonic effect shift to a lower energy level at 11 eV than without the excitonic effect at 13.5 eV. The electron charge distribution is computed by fixing the hole position. Finally, we suggest that type II o-BC2N is promising for the application of optoelectronic semiconductors.
This article reports magnetization and specific heat capacity anomalies in one dimensional diluted magnetic semiconductors observed at very low temperatures. Based on quantum field theory double time ...temperature dependent Green function technique is employed to evaluate magnon dispersion and the time correlation function. It is understood that magnon-photon coupling and magnetic impurity concentration controls both, such that near absolute temperature magnetization is nearly zero and abruptly increase to saturation level with decreasing magnon-photon coupling strength. We also found out dropping of magnetic specific heat capacity as a result of increase in magnetic impurity concentration x, perhaps because of inter-band disorder that would suppress the enhancement of density of spin waves.
Using first‐principles calculations, biaxial tensile (ϵ=2 and 4 %) and compressive (ϵ=−2 and −4 %) straining of Na2MnSiO4 lattices resulted into radial distance cut offs of 1.65 and 2 Å, ...respectively, in the first and second nearest neighbors shell from the center. The Si−O and Mn−O bonds with prominent probability density peaks validated structural stability. Wide‐band gap of 2.35 (ϵ=0 %) and 2.54 eV (ϵ=−4 %), and narrow bandgap of 2.24 eV (ϵ=+4 %) estimated with stronger coupling of p–d σ bond than that of the p–d π bond, mainly contributed from the oxygen p‐state and manganese d‐state. Na+‐ion diffusivity was found to be enhanced by three orders of magnitude as the applied biaxial strain changed from compressive to tensile. According to the findings, the rational design of biaxial strain would improve the ionic and electronic conductivity of Na2MnSiO4 cathode materials for advanced rechargeable sodium‐ion batteries.
Biaxial tensile and compressive straining of the Na2MnSiO4 framework has been investigated using first‐principle calculations. Na+‐ion diffusivity was found to be enhanced by three orders of magnitude as the applied biaxial strain changed from compressive to tensile. Rational design of biaxial strain could thus be used to improve Na2MnSiO4 cathode materials for advanced rechargeable sodium‐ion batteries.
Abstract
The dream of realizing room temperature superconductivity is one of the most challenging problems in condensed matter physics. Currently, materials with dense hydrogen contents at high ...pressures hold great promise for realizing room temperature superconductivity. In particular, pressurized alkaline earth metal hydrides received particular attention following the recently predicted sodalite-like calcium hydride (CaH
6
) with predicted Tc about 261 K above a pressure of 150 GPa; and magnesium hydride (MgH
6
) with predicted Tc about 270 K above 300 GPa. In this paper, we studied magnesium hydride (MgH
4
) with tetragonal (I4/mmm) type symmetry, and we found that this structure shows the highest
T
c
≅
313
K
at a pressure of 280 GPa which is higher than that of MgH
6
. Using density-functional perturbation theory (DFPT), the superconducting transition temperature, electron-phonon coupling, Eliashberg spectral function, and the logarithmic average frequency were computed. Our results reveal that, the computed values are reasonably in agreement with previous estimates.
This article reports the crystal structure, impurity formation energy, electronic property, magnetic property, and dopant configuration site dependence of ferromagnetic temperature Tc of anatase ...(Ti15FeO32, Ti14Fe2O32, and Ti13Fe3O32) by first-principles calculations based on density functional theory (DFT) with Hubbard onsite correction (DFT+U). The estimated formation energy validated the structural stability of the Fe-doped TiO2 with 2.08% (Ti15FeO32), 4.17% (Ti14Fe2O32), and 6.25% (Ti13Fe3O32) concentrations at the Ti sites. The electronic structure analysis reveals that the bandgap in the doped system changed from a wide bandgap of 3.23 eV (pristine TiO2) to slightly lower bandgaps of 3.13, 3.08, and 3.04 eV with Fe concentrations of 2.08%, 4.17%, and 6.25%, respectively. The calculated partial density of states also show the hybridization of O with 2p- and Fe 3d-orbitals near the conduction band minimum and generate the impurity energy level reducing the bandgap. Furthermore, the estimated Curie temperature (Tc) varied depending on the Fe–Fe interactions, the concentration of the Fe dopants, and doping sites. For instance, Tc is calculated to be 343.57 K for 2.08% Fe at the symmetric point of the crystal while estimated to be 323.84 and 393.297 K for 4.17% at the nearest neighbor and the next-nearest neighbor configurations. Due to the increase of the Fe concentration to 6.25%, the calculated Tc monotonically improved to 342.5 and 513.174 K at the nearest neighbor and the next-nearest neighbor of the Fe-site, respectively. These indicate that all the calculated findings estimate the ferromagnetic transition temperature Tc to above room temperature. Moreover, the system’s total magnetization reveals the augmentation of a number of unpaired electrons as a result of rise in oxygen vacancies and, hence, there could be more holes when the Fe content gets higher, perhaps generating more bound magnetic polarons that favor the critical temperature, Tc.
Starting with a Kondo lattice model type Hamiltonian, the effects of the magnetic field, electric field, and magnetic anisotropic energy on the magnetic properties of the Fe/GaSb diluted magnetic ...semiconductor are studied. The analytical technique is employed to analyze magnon dispersion, magnetization, and critical temperature, Tc. The enhancement of the temperature with increasing impurity concentration x and/or with the magnetic field and electric field is established, which is in good agreement with recent experimental observations. It is clearly shown that magnon dispersion and magnetization can be controlled with these fields applied, magnetic anisotropic energy, and impurity concentration alternatively or all together. Due to the inclusion of the magnetic anisotropic energy, we could identify a significant escalation of magnon dispersion/bandgap energy and a slight reduction of magnetization.
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