Light and Matter Id / Licht und Materie Id

Zusatztext

The dynamical properties of solids have recently attracted renewed interest in connection with the increasing understanding of phase transitions and re lated phenomena. In particular, soft modes or, more generally, phonon 'anom alies' seem to play an important role in structural and electronic phase tran sitions, such as ferroelectric or superconducting transitions. The understanding of the mechanisms responsible for the occurrence of unusually low frequencies in phonon spectra requires a detailed analysis of the microscopic forces governing the lattice vibrations. Of particular importance is the influence of the electron lattice interaction in the adiabatic approximation which in many cases is the origin of peculiarities in the phonon self-energy. In this work the vibrational spectra of pure non-metals and of those con taining point defects are investigated. ' In these materials the interrelation be tween the pseudo-harmonic forces (determining the phonon dispersion re lations) and the non-linear anharmonic and electron-phonon forces (as they act in infrared and Raman spectra) is most obvious and can be quantitatively analysed in terms of appropriate models. The main task is to arrive at a physically correct treatment of electronic degrees of freedom, as for example in an electronic 'shell' model, which leads to the description of phonon spectra in terms of long-range polarizabilities and short-range deformabilities. The pur pose of our review is to stimulate further investigations which, we hope, will result in explicit relations between the parameters of the semi-microscopic models and the matrix elements from the electronic band structure.

Autorenportrait

InhaltsangabeVibrational Infrared and Raman Spectra of Non-Metals.- A. Introduction.- 1. Historical survey.- 2. Outline of the theory of infrared absorption and Raman scattering.- a) Macroscopic aspects.- b) Microscopic aspects.- B. Phonons in insulators.- 3. General properties of phonons.- a) Dynamic and thermodynamic stability of solids.- b) The adiabatic approximation.- c) Force constants.- d) Symmetry properties of phonons.- e) The pseudo-harmonic approximation.- 4. Ionic crystals.- a) The rigid-ion model.- b) Dipole models.- c) The breathing shell model.- d) Ionic deformabilities.- e) Non-central and many-body forces and the elastic properties of crystals.- 5. Covalent crystals.- a) Formal force constants and general properties.- b) Dipole models.- c) Bond-charge models.- d) Valence force fields.- e) Crystals of partially ionic and partially covalent character.- f) Sum rule of lattice vibrations.- 6. Microscopic theory, models, and macroscopic quantities.- a) Overlap theory.- b) The dielectric function method.- c) The direct 'frozen-in' phonon approach.- d) Charges and polarizabilities of ions and bonds.- e) Electric fields and effective charges in ionic solids.- f) Fields and charges in covalent solids.- g) The microscopic description of charges and fields.- C. Interaction of photons with matter.- 7. Theory of interaction of photons with particles.- a) Non-relativistic theory of inelastic scattering.- b) Gauge invariance in electromagnetic interaction.- c) Dielectric constant of electrons.- d) Light scattering by electrons.- e) Interaction of photons with electrons and ions.- f) Polaritons in the harmonic approximation.- 8. Infrared absorption and dielectric response.- a) Dielectric susceptibility.- b) Absorption of radiation (fluctuation-dissipation theorem).- c) Frequence-dependence and thermodynamic definitions of the susceptibility, sum rules.- d) Static susceptibility.- 9. Raman scattering of light.- a) Introduction.- b) Quantum theory of spontaneous Raman scattering.- c) Adiabatic representation.- d) Polarizability theory.- e) Green function theory of Raman scattering.- f) The ?4 law.- g) Polariton picture of light scattering.- h) Resonant Raman scattering (RRS).- i) Rayleigh, Brillouin, and Hyper-Raman scattering.- D. Expansion theory of susceptibilities and polarizabilities.- 10. General lattice potential.- a) The undeformed lattice.- b) The lattice in a static electric field and under deformation.- 11. Lattice dipole moment.- a) The undeformed lattice.- b) The lattice in a static electric field and under deformation.- 12. Lattice and electronic susceptibility.- a) Formal expansion of the susceptibility.- b) The harmonic approximation.- c) Anharmonic susceptibility.- d) The anharmonic dispersion oscillator.- e) The damping function.- f) The renormalized dipole moment.- g) The general form of the lattice susceptibility.- h) Coupling of dispersion oscillators.- i) Anharmonic coupling parameters.- j) The susceptibility under external pressure and in a static field.- 13. Lattice polarizability and Raman scattering.- a) Formal expansion of the electronic susceptibility.- b) Harmonic approximation.- c) Anharmonie treatment.- d) Raman scattering in cubic crystals.- e) Raman coupling parameters.- f) Effects of static fields and external pressure.- E. Interpretation of experimental spectra.- 14. Model theory of infrared absorption and Raman scattering.- a) General features of infrared and Raman processes.- b) Microscopic and model treatment of electron-phonon interaction.- c) Shell model treatment of Raman scattering.- d) Bond charge and bond polarizability in infrared and Raman processes.- 15. Infrared spectra of ionic crystals.- a) Qualitative classification of infrared spectra.- b) The infrared spectra of alkali halides: anharmonic effects.- c) Critical point analysis.- d) Density of states approximation.- e) The effect of short-range cubic anharmonicity.- f) The effect of quartic and higher anharmonicity.- g) Coulomb anharmonicity

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