Cooperative Phenomena in Jahn Teller Crystals

This book by Kaplan and Vekhter brings together the molecular world of the chemist with the condensed matter world of the physicist. Prior to the collapse of the Soviet Union, chemists in the West devoted lit to relationships between molecular electronic structure and tle attention solid-state vibronic phenomena. Treating quantum mechanical problems wherein the adiabatic Born-Oppenheimer approximation fails was done by "brute force. " With bigger and better computers available in the West, molecular orbital calculations were done on observed and conceived static structures with little concern for any cooperativity of vibrational behavior that might connect these states. While it had long been understood in the West that situations do occur in which different static structures are found for molecules that have identical or nearly identical electronic structures, little attention had been paid to understanding the vibrational states that could connect such structures. It was easier to calculate the electronic structure observed with several possible distortions than to focus on ways to couple electronic and vibrational behavior. In the former Soviet Union, computational power was not as acces sible as in the West. Much greater attention, therefore, was devoted to conserving computational time by considering fundamental ways to han dle the vibrational connectivity between degenerate or nearly degenerate electronic states.

Contenu

1. The JahnTeller Effect.- 1.1. The JahnTeller Theorem.- 1.2. Electron-Vibration Coupling in the Case of Electronic Degeneracy.- 1.3. Typical JahnTeller Situations.- 1.4. Interaction with Rotations and Quadratic Vibronic Coupling.- 1.5. Situations Similar to the JahnTeller Effect.- 1.6. Manifestation of the JahnTeller Effect.- 1.7. Examples of JahnTeller Systems.- References.- 2. Interaction of JahnTeller Centers.- 2.1. Direct Exchange in Orbital Degeneracy.- 2.2. Superexchange in Orbital Degeneracy.- 2.3. Indirect Exchange through Conduction Electrons.- 2.4. Multipole Interactions.- 2.5. Interaction of Ions through the Exchange of Virtual Phonons.- 2.6. The Cooperative JahnTeller Effect.- 2.7. Types of JahnTeller Orderings.- References.- 3. The Elastic Properties of Crystals with JahnTeller Structural Phase Transitions.- 3.1. Tetragonal ? Orthorhombic Phase Transitions with Twofold-Degenerate States.- 3.2. Cubic ? Tetragonal Structural Phase Transitions in Crystals with a Threefold-Degenerate Ionic Ground State.- 3.3. Structural Phase Transitions Induced by the Cooperative Pseudo JahnTeller Effect.- 3.4. Characteristics of Structural Phase Transitions in Singlet-Doublet-Singlet Systems.- 3.5. The Cooperative JahnTeller Effect in Dynamic Electron-Phonon Coupling.- 3.6. Anomalies of Nonsoft Elastic Constants in JahnTeller Structural Phase Transitions.- References.- 4. Mutual Influence of Distortive, Magnetic, and Electric Dipole Orderings in JahnTeller Elastics.- 4.1. Mutual Quenching of Structural and Magnetic Orderings.- 4.2. Mutual Enhancement of Structural and Magnetic Orderings.- 4.3. Magnetic Anisotropy and Noncollinearity of Magnetic Structures.- 4.4. High Spin-Low Spin Phase Transitions.- 4.5. Domain Walls inthe Competition of Structural and Magnetic Orderings.- 4.6. Interrelationship between Acoustical and Dielectric Anomalies in Ferrodistortive Antiferroelectrics.- 4.7. Antiferrodistortive Ferroelectric Transitions.- 4.8. Interrelationship between Distortive and Electric Dipole Structures in Noncentrosymmetric Crystals.- 4.9. Anomalies of the Transverse Dielectric Susceptibilities.- 4.10. Coexistence of Spontaneous Strains of Different Symmetries in Mixed Crystals.- References.- 5. JahnTeller Crystals in External Fields: Phase Diagrams and Properties.- 5.1. Phenomenological Description of Striction in JahnTeller Crystals.- 5.2. Dynamic Magnetostriction of Systems with Mutual Suppression of Magnetic and Distortive Interactions.- 5.3. Dynamic Magnetostriction of Systems with Mutual Enhancement of Magnetic and Distortive Interactions.- 5.4. Anomalous Electrostriction and Magnetoelectric Effects.- 5.5. Metamagnetoelasticity of Antiferroelastics.- 5.6. Structural Transitions Stimulated by a Magnetic Field.- 5.7. Magnetodistortive Phase in JahnTeller Antiferromagnetics and Its Properties.- 5.8. Anomalous Magnetic Nonlinearity of Elastics.- 5.9. Electric Field-Induced Ferroelastic-Antiferroelastic Phase Transition.- 5.10. Reorientational Structural Phase Transitions in JahnTeller Crystals.- References.- 6. The Dynamics of JahnTeller Crystals.- 6.1. Electron-Phonon Modes and Sound Absorption.- 6.2. Frequency Dependence of the Response Functions.- 6.3. Mixed Electron-Phonon Modes in Crystals with Several JahnTeller Ions in the Unit Cell.- 6.4. Hyperfine Interaction and Nuclear Sound Absorption.- 6.5. Parametric Sound Generation.- 6.6. The Central-Peak Problem.- 6.7. Transport Phenomena in JahnTeller Crystals; Thermal Conductivity.- References.