Dephasing of Local Vibrations in a Planar Lattice of Adsorbed Molecules

We investigate anharmonically coupled high- and low-frequency excitations in a planar lattice of adsorbed molecules interacting with phonons of a crystal. Dephasing of high-frequency local vibrations by low-frequency resonance modes is described in terms of the temperature Green's function. The equations obtained are solved, first, with a small ratio of the anharmonic-coupling coefficient for high- and low-frequency modes to the resonance width, and second, in the low-temperature limit. High-frequency spectral-line positions and widths depend on dispersion laws and resonance-mode lifetimes. It is shown that lateral interactions of low-frequency modes of adsorbed molecules can lead to a significant narrowing of high-frequency spectral lines, which is consistent with experimental data.

Excitonic Enhanced Optical Gain Of GaN/AlGaN Quantum Wells With Localized States

We have evaluated the optical gain of GaN/AlGaN quantum well structures with localized states, taking into account the Coulomb interaction. The localized states axe introduced in the well as quantum dot-like subband states. We have used the temperature Green's function formalism to treat the many-body effects and have found a new excitonic enhancement of the optical gain involved the localized states. This enhancement is stronger than the conventional Coulomb enhancement. It might play an important role to reduce the threshold carrier density.

SPEED OF SOUND IN NUCLEAR MATTER AND SKYRME EFFECTIVE INTERACTIONS

Using a nuclear equation of state derived from a finite-temperature Green’s function method and the Skyrme effective interactions SkI, SkIII and SkM*, we have calculated the speed of sound in symmetric nuclear matter. For certain densities and temperatures, this speed is found to become super-luminous. Causal boundaries in the density-temperature plane are determined, and they indicate that SkM* is a more desirable effective interaction than SkI and SkIII. Comparison with a similar calculation by Osnes and Strottman is made.

CRITICAL NEUTRON-PROTON ASYMMETRY OF HOT NUCLEAR MATTER

We derive an equation of state for asymmetric nuclear matter at finite temperature, using the Skyrme effective nucleon-nucleon interaction and a mean field approach based on a real-time finite temperature Green’s function method with a normal pair cutoff approximation. With the temperature held constant, it is found that nuclear matter can exist only in the gaseous phase when its neutron excess coefficient a has surpassed a certain critical value αc. We have calculated αc for a number of different Skyrme effective interactions. Phase diagrams involving a are obtained, and a low-density equation for the phase boundary is derived.