PHONONS AND THEIR INTERACTIONS WITH ELEMENTARY EXCITATIONS.
Abstract
A many-body theory for plasma effects in solids based on an interacting electron gas model has been derived which is similar to the polariton theory. In this manner the quantum helicon dispersion relation was obtained and effects of many-body interactions and correlations were studied. The same methods were applied to magnetic systems and the coupled electron-magnon and photon-magnon modes were discussed. The phonon dispersion of bismuth has been calculated using a shell model and a quadrupole mode. In both models long-range electrostatic forces are included in addition to the short-range forces which extend to only first and second nearest neighbor interactions. Comparisons are made with experimental results. To study the effect of disorder on the phonon spectrum a three dimensional lattice with isotopic impurities was studied. An analytic calculation was made that is valid for an arbitrary concentration of impurity atoms. Variational methods for decoupling the equations of motion of many-body systems were investigated. The most fruitful result is a variational approximation to the spectral densities. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 23, 1969
- Accession Number
- AD0704147
Entities
People
- H. Hartmann
Organizations
- New York University