Narrow Results

The donor ionization energies in a quantum well and quantum dot with finite and infinite barriers are estimated for different well dimensions. Using the effective mass (EM) approximation, calculations are presented with constant effective mass and position dependent effective masses that are different for finite and infinite cases. Our results reduce to an approximate form used by X. H. Qi et al., Phys. Rev. B58 (1998) 10578 in the finite barrier model and that of L. E. Oliveira and L. M. Falicov, Phys. Rev. B34 (1986) 8676 in the infinite barrier case. Results are presented by taking the GaAs quantum well as an example. The use of constant effective mass of 0.067m₀ is justified for well dimensions ≥a* where a* is an effective Bohr radius which is about 100 Å. While Qi et al. found a maximum of 22% variation in the binding energies due to mass variation, we obtained nearly 100% variation when mass variations are included correctly.

We review old and new results on the Fröhlich polaron model. The discussion includes the validity of the (classical) Pekar approximation in the strong coupling limit, quantum corrections to this limit, as well as the divergence of the effective polaron mass.

The aim of this work is to examine the influence of the type and concentration of an electrolyte solution on the optical characteristics of CdS nanoparticles produced by the sonochemical approach. The optical characteristics of the samples were examined using an Ultraviolet–Visible (UV–Vis) spectrophotometer in order to calculate the bandgap value. Acquired samples were examined on how to change the bandgap at various concentrations within various electrolyte solutions in order to ascertain the effects of various ambiences. Cadmium nitrate tetrahydrate (Cd (NO${}_3{)}_2\cdot$4H₂O), cadmium acetate dihydrate (Cd(CH₃COO)${}_2\cdot$2H₂O) and sodium chloride (NaCl) water solutions were utilized as electrolytes in three different environments. When the sample was exposed to a different environment, its energy spectrum changed. Measurements show that raising the concentration of various electrolyte solutions decreased the bandgap values of the samples.

Phenomena such as pulsar frequency glitches are believed to be attributable to differential rotation of a current of "free" superfluid neutrons at densities above the "drip" threshold in the ionic crust of a neutron star. Such relative flow is shown to be locally describable by adaption of a canonical two-fluid treatment that emphasizes the role of the momentum covectors constructed by differentiation of action with respect to the currents, with allowance for stratification whereby the ionic number current may be conserved even when the ionic charge number Z is altered by beta processes. It is demonstrated that the gauge freedom to make different choices of the chemical basis determining which neutrons are counted as "free" does not affect their "superfluid" momentum covector, which must locally have the form of a gradient (though it does affect the "normal" momentum covector characterizing the protons and those neutrons that are considered to be "confined" in the nuclei). It is shown how the effect of "entrainment" (whereby the momentum directions deviate from those of the currents) is controlled by the (gauge-independent) mobility coefficient , estimated in recent microscopical quantum mechanical investigations, which suggest that the corresponding (gauge-dependent) "effective mass" m_⋆ of the free neutrons can become very large in some layers. The relation between this treatment of the crust layers and related work (using different definitions of "effective mass") intended for the deeper core layers is discussed.

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.

The status of relativistic nuclear many-body calculations of nuclear systems to be built up in terms of protons and neutrons is reviewed. In detail, relativistic effects on several aspects of nuclear matter such as the effective mass, saturation mechanism, and the symmetry energy are considered. This review will especially focus on isospin asymmetric issues, since these aspects are of high interest in astrophysical and nuclear structure studies. Furthermore, from the experimental side these aspects are experiencing an additional boost from a new generation of radioactive beam facilities, e.g., the future GSI facility FAIR in Germany or SPIRAL2 at GANIL/France. Finally, the prospects of studying finite nuclei in microscopic calculations which are based on realistic NN interactions by including relativistic effects in calculations of low momentum interactions are discussed.

Based on the effective-mass concept, we perform the Faddeev calculations for a low-lying spectrum of 3$\alpha$ states in ${}^{12}$C nucleus. A three-body potential is used to describe the known breaking of the 3$\alpha$-cluster structure in the nucleus. We show that the contribution of the three-body potential to the Hamiltonian can be compensated by increasing/decreasing the $\alpha$-particle free mass. The effective-mass values are adjusted to reproduce the experimental data for the ${}^{12}$C nucleus. The energy dependence of the effective mass and the correlation to a three-body potential are discussed. We show that the coupling between the $0^{+}$ ($2^{+}$) levels forms a specific picture of anti-crossing on the energy/effective-mass plane.

According to the first-principle method for the density functional theory (DFT), combined with the hybrid functional (HSE06), the electronic structure and effective mass of Mg-doped GaN and Mg–Fe co-doped GaN systems are calculated, and the stability of the co-doped structure is analyzed from the perspective of formation energy and phonon dispersion. The results showed that the introduction of Fe improved the characteristics of GaN:Mg system: the GaN material doped with Mg merely would cause the material’s valence band maximum to exceed the Fermi level, presenting a $p$-type conduction; the addition of Fe increased the energy band density of the system, and the insulation of the material was enhanced due to the higher energy level of the introduced impurity. Furthermore, the influence of Mg doping on the magnetic properties of GaN-based diluted magnetic semiconductor (DMS) was considered as well, with the magnetic moment obtained from co-doping Mg–Fe slightly reduced by a comparison of that of GaN:Fe measured by our research group. The results showed that the difference in the effective mass of GaN:Mg:Fe system in different directions was smaller than that of GaN:Mg system, indicating that the anisotropy of the system was reduced by doping Fe.

In this paper, for the first time, changes in the effective mass (EM) of electron and hole with mole fraction are taken into account for extracting the benchmarking parameters of analog/radio frequency (RF) and high-frequency noise performance of junctionless (JL)-Ga${}_x$In${}_{1-x}$As/GaAs via simulation. In the JL-Ga${}_x$In${}_{1-x}$As/GaAs structure, considering changes in the effective mass with mole fraction is called a with-EM state, while the JL-Ga${}_x$In${}_{1-x}$As/GaAs structure without considering the changes in effective mass with mole fraction is called a without-EM state. The simulation results show that, per $x=0.5$, the maximum transconductance in the with-effective mass (EM) state is $G_{m,max}=2.3$ mS/$\mu$m, which is reduced by 8% compared to the without-EM state. The JL-Ga${}_{0.5}$In${}_{0.5}$As/GaAs device in the with-EM state has the unity gain cutoff frequency of $f_T=900$ GHz, minimum noise figure of $N_{f,min}=0.29$ db, and available associated gain of $G_{\mathrm{\text{ass}}}=23.84$ db. The $f_T$ and $G_{\mathrm{\text{ass}}}$ parameters in the with-EM state decreased by 10% and 38%, respectively, compared to the without-EM state. Moreover, $N_{f,min}$ in the with-EM state increased by 65% compared to the without-EM state. Our simulation results indicated that an increase in electron effective mass with the increased $x$ can limit the analog/RF frequency and high-frequency noise performance of the JL-Ga${}_x$In${}_{1-x}$As/GaAs device.

The work theoretically calculated the electronic structure and electrical transport properties of two configurations of single-walled MoS₂ nanotubes: armchair nanotubes (ANTs) and zigzag nanotubes (ZNTs) based on the density functional theory and Boltzmann transport method. ANTs have an indirect one. while ZNTs have a direct bandgap structure. The Seebeck coefficient ($S$), electrical conductivity ($\sigma )$ and power factor ($S^2\sigma )$ were calculated as a function of carrier concentration, chemical potential and temperature using the Boltzmann transport method. The calculated power factor ($S^2\sigma$) indicates that the most promising electronic properties were exhibited by $p$-type ANTs and $n$-type ZNTs. The $S^2\sigma$ of narrow bandgap (6, 6) (7, 7) (8, 8) semiconductors reached $4.0\times 10^{-4}$, $6.3\times 10^{-4}$ and $6.3\times 10^{-4}\mu$WK${}^{-2}$m${}^{-1}$ at room-temperature, respectively. (7, 7) nanotube have a maximum power factor of $3.44\ast 10^{-3}\mu$WK${}^{-2}$m${}^{-1}$ at 950 K, and the maximum power factor of ANTs is almost twice that of ZNTs.

Electronic and thermoelectric properties of pure In₂O₃ and In_1.5T_0.5O₃ (T=Sc, Y) alloys including the band gap, the electrical and thermal conductivity, Seebeck coefficient and figure of merit have been investigated using semi-classical Boltzmann transport theory. The calculated results indicated that substituting indium atoms by these dopants have a significant influence on the electronic properties of alloyed In₂O₃ crystals. Substitution of Sc and Y atoms for In atoms increases the band gaps and Seebeck coefficient. The intrinsic relations between electronic structures and the transport performances of In₂O₃ and its alloys with Sc and Y are also discussed.

The electronic structure, density of states (DOS), effective mass are calculated for tetragonal TlInSe₂ from first principle in the framework of density functional theory (DFT). The electronic structure of TlInSe₂ has been investigated by Quantum Wise within GGA. The calculated band structure by Hartwigsen–Goedecker–Hutter (HGH) pseudopotentials (psp) shows both the valence band maximum and conduction band minimum located at the T point of the Brillouin zone. Valence band maximum at the T point and the surrounding parts originate mainly from 6s states of univalent Tl ions. Bottom of the conduction band is due to the contribution of 6p-states of Tl and 5s-states of In atoms. Calculated DOS effective mass for holes and electrons are $m_{{\mathrm{\text{DOS}}}_h}^{\ast }=0.830m_e$, $m_{{\mathrm{\text{DOS}}}_h}^{\ast }=0.492m_e$, respectively. Electron effective masses are fairly isotropic, while the hole effective masses show strong anisotropy. The calculated electronic structure, density of states and DOS effective masses of TlInSe₂ are in good agreement with existing theoretical and experimental results.

Research study of volt-amperage properties (VAP) of $\mathrm{\text{Ca}}{({\mathrm{\text{Al}}}_{0.1}{\mathrm{\text{Ga}}}_{0.9})}_2{\mathrm{\text{S}}}_4:{\mathrm{\text{EuF}}}_3$ crystals determined the mechanism of current flow though the studied samples and this mechanism is based on barrier Schottky emission and emission of Franklin–Paul. The dielectric constant of the material, height of the potential barrier on metal–semiconductor border, concentration of the traps and the effective mass of electrons are calculated.

We construct first-order Darboux transformations for stationary Schrödinger equations with position-dependent (effective) mass and energy-dependent potential. We point out characteristic differences to the corresponding Darboux transformation for constant mass.¹⁴

The ground state properties and the structural phase transformation of tin dioxide (SnO₂) have been investigated using first principle full potential-linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). We used local density approximation (LDA) and the generalized gradient approximation (GGA), which are based on exchange-correlation energy optimization, to optimize the internal parameters by relaxing the atomic positions in the force directions and to calculate the total energy. For band structure calculations, we utilized both the Engel-Vosko's generalized gradient approximation (EVGGA), which optimizes the exchange-correlation potential, and also GGA. From the obtained band structures, the electron (hole) valance and conduction effective masses are deduced. For compressed volumes SnO₂ is shown to undergo two structural phase transitions with increasing pressure from the rutile- to the CaCl₂-type phase at 12.4 GPa and to a cubic phase, space group at 22.1 GPa. The calculated total energy allowed us to investigate several structural properties, in particular, the equilibrium lattice constants, bulk modulus, cohesive energy, interatomic distances and the angles between different atomic bonds. In addition, we discuss the bonding parameter in term of charge density, which show the localization of charge around the anion side.

In this paper, on the basis of Huybrechs' strong-coupled polaron model, Tokuda modified linear-combination operator and the unitary transformation methods are used to study the properties of the strong-coupled polaron considering the influence of Rashba effect, which is brought by the spin-orbit (SO) interaction, in the asymmetric quantum dot (QD). The expressions of the effective mass as a function of the transverse and longitudinal confinement strengths, the velocity and the vibration frequency were derived. Numerical calculation on the RbCl QD, as an example, is performed and the results show that the total effective mass of the polaron is composed of three parts. The interaction between the orbit and the spin with different directions has different effects on the effective mass of the polaron.

In this paper, we construct the Hamiltonian description of the closed vortex filament dynamics in terms of non-standard variables, phase space and constraints. The suggested approach makes obvious interpretation of the considered system as a structured particle that possesses certain external and internal degrees of the freedom. The constructed theory is invariant under the transformation of Galilei group. The appearance of this group allows for a new viewpoint on the energy of a closed vortex filament with zero thickness. The explicit formula for the effective mass of the structured particle “closed vortex filament” is suggested.

For more than three decades, the inner crust of neutron stars, formed of a solid lattice of nuclear clusters coexisting with a gas of electrons and neutrons, has been traditionally studied in the Wigner-Seitz approximation. The validity of this approximation is discussed in the general framework of the band theory of solids, which has been recently applied to the nuclear context. Using this novel approach, it is shown that the unbound neutrons move in the crust as if their mass was increased.