Browsing by Subject "Waveform"
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Item Open Access Anharmonic line shift and linewidth of the Raman modes in TlInS2 layered crystals(John Wiley & Sons Ltd., 2004) Yuksek, N. S.; Gasanly, N. M.; Aydınlı, AtillaThe temperature dependence of the unpolarized Raman spectra from TlInS 2 layered crystal was measured between 10 and 300 K. The analysis of the experimental data showed that the temperature dependences of wavenumbers and linewidths are well described by considering the contributions from thermal expansion and lattice anharmonicity. The purely anharmonic contribution (phonon-phonon coupling) was found to be due to three-phonon processes. This work demonstrates that the two Raman modes at 280.9 and 292.3 cm-1 exhibit changes toward high wavenumbers as the temperature is raised from 10 to 300 K.Item Open Access Dynamic correlations in double-layer electron systems(The American Physical Society, 2001) Tanatar, Bilal; Davoudi, B.We study the effects of dynamic correlations on the ground-state properties of a double-layer two-dimensional electron gas within the quantum Singwi-Tosi-Land-Sjölander theory (STLS). The intralayer and interlayer static structure factors, the pair-correlation functions, and the wave vector and frequency-dependent local-field factors have been calculated for a range of electron densities and layer separations. We find that the local-field factors have an oscillatory frequency dependence and the magnitude of interlayer local-field factors is about an order of magnitude smaller than that of the intralayer. Our results are compared with the random-phase approximation and the static STLS approximation to assess the importance of dynamical correlations. We also calculate the dispersion relations for the optical and acoustic plasmons and the damping of these modes to compare them with other mean-field theories, and we comment on the relevance of our results to the recent experiments.Item Open Access Negative refraction by photonic crystals(Nature, 2003) Cubukcu, E.; Aydin, K.; Özbay, Ekmel; Foteinopoulou, S.; Soukoulis, C. M.