We discuss the determination of the heavy charm- and bottom-quark masses from the sum rule approach as well as the determination of the strong coupling constant from the measurable R-ratio, hadronic τ-lepton decays a...
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Using the alpha-T-3 model, we carried out analytical and numerical calculations for the static and dynamic polarization functions in the presence of a perpendicular magnetic field. The model involves a parameter alpha...
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Using the alpha-T-3 model, we carried out analytical and numerical calculations for the static and dynamic polarization functions in the presence of a perpendicular magnetic field. The model involves a parameter alpha which is the ratio of the hopping strength from an atom at the center of a honeycomb lattice to one of the atoms on the hexagon to the hopping strength around its rim. Our results were employed to determine the longitudinal dielectric function and the magnetoplasmon dispersion relation. The magnetic field splits the continuous valence, conduction and flat energy subband into discrete Landau levels which present significant effects on the polarization function and magnetoplasmon dispersion. This includes the fact that the energies of the Landau levels are valley dependent which leads to different behaviors of the polarization function as the hopping parameter alpha(or phi= tan(-1)alpha) is reduced continuously toward zero. This essential critical behavior of the polarization function leads to a softening of a magnetoplasmon mode. We present results for a doped layer in the integer quantum Hall regime for fixed hopping parameter alpha and various magnetic fields as well as chosen magnetic field and different alpha in the random phase approximation.
The linear optical response of semiconductors has been studied beyond the density-functional theory with ab initio pseudopotentials and the random-phase approximation. Effects of the macroscopic local fields and the m...
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The linear optical response of semiconductors has been studied beyond the density-functional theory with ab initio pseudopotentials and the random-phase approximation. Effects of the macroscopic local fields and the microscopic exchange-correlation interaction are included in the description of the optical spectra. Quasiparticle corrections to the single-particle energies have been added in the polarization function. Numerical calculations are performed for the group-IV materials Si, SiC, and diamond as model substances. In the static limit and in the low-frequency region, corrections due to the local fields reduce the dielectric function, whereas inclusion of the exchange-correlation interaction enhance the oscillator strengths. In the high-energy region these effect have a more complex character, and the signs of the relevant corrections change in dependence on the photon energy. The effects considered strongly modify the plasmon resonance in the energy-loss function. The results obtained are discussed in comparison with theoretical and experimental data available.
We present a numerically efficient approach to solve the Bethe-Salpeter equation for the polarization function. Rather than from the usual eigenvalue representation, the macroscopic polarizability is obtained from the...
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We present a numerically efficient approach to solve the Bethe-Salpeter equation for the polarization function. Rather than from the usual eigenvalue representation, the macroscopic polarizability is obtained from the solution of an initial-value problem. This reduces the computational effort considerably and allows for calculating excitonic and local-field effects in optical spectra of complex systems consisting of many atoms. As an example we investigate the optical anisotropy of the monohydride Si(001)(2×1) surface. While excitonic effects influence the surface optical properties considerably, the local-field effect induced changes are minimal.
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