Structural phase transitions in layered transition metal compounds

Microscopic Theory of Structural Phase Transitions in Layered Transition-metal Compounds. - 1. Introduction. - 2. General theory of electron-lattice interaction and lattice dynamics based on the nonorthogonal tight-binding approximation. - 2.1. Electron-lattice interaction. - 2.2. Generalized electronic susceptibility. - 2.3. Interatomic force, phonon dispersion, and lattice instability. - 2.4. Electronic structure of the CDW state. - 2.5. Other methods of lattice dynamical calculation. - 3. 1T-type transition-metal dichalcogenides. - 3.1. TiSe2. - 3.1. 1. Formation of superlattice. - 3.1. 2. Electronic structure. - 3.1. 3. Electron-lattice interaction and generalized electronic susceptibility. - 3.1. 4. Lattice dynamics. - 3.1. 5. The CDW state. - 3.2. TiS2. - 3.3. Mixed compounds. - 3.4. VSe2 and CrSe2. - 3.4.1. Summary of experimental evidence regarding structural transformation. - 3.4.2. Electronic structure. - 3.4.3. Electron-lattice interaction and lattice instability. - 3.5. TaS2 and TaSe2. - 3.5.1. Summary of successive phase transitions. - 3.5.2. Electronic structure. - 3.5.3. Lattice instability. - 4. 2H-type transition-metal dichalcogenides. - 4.1. Formation of superlattice. - 4.2. Electronic structure. - 4.3. Electron-lattice interaction and generalized electronic susceptibility. - 4.4. Lattice dynamics and phonon anomaly. - 4.5. Discussion. - 5. Transition-metal trichlorides MCl3 (M = Ti, V, Cr). - 5.1. Summary of experimental results. - 5.2. Electronic structure. - 5.2.1. Tight-binding calculation. - 5.2.2 The Wannier function. - 5.2.3 Estimation of band parameters. - 5.3. Electron-lattice interaction and lattice instability in TiC13. - 5.3.1. Generalized electronic susceptibility. - 5.3.2. Effective d-electron-lattice interaction and lattice instability. - 5.3.3. The transition temperature. - 5.3.4. Some remarks regarding VCl3 and CrCl3. - 5.4. Phase transition. - 5.4.1. Calculation of free energy. - 5.4.2. Magnetic susceptibility. - Appendix A. Perturbation theory in nonorthogonal representation. - Appendix B. Electronic free energy expansion in the adiabatic approximation and derivation of generalized electronic susceptibility. - Appendix C. Froehlich model and Bloch model. - Appendix D. Expressions for the overlap and transfer integrals and their derivatives in terms of Slater-Koster integrals. - Microscopic Theory of Effects of Lattice Fluctuation on Structural Phase Transitions. - 1. Introduction. - 2. Formulation. - 2.1. Hamiltonian and Green's functions for electron and phonon systems. - 2.1. 1. Hamiltonian. - 2.1. 2. Thermal Green's functions for electrons. - 2.1. 3. Thermal Green's functions for phonons. - 2.1. 4. Self-energy ? and polarization function ? - 2.2. Random phase approximation. - 2.3. Mode-mode coupling. - 2.3.1. Lattice fluctuation. - 2.3.2. Transition temperature. - 2.3.3. Coherence length. - 2.3.4. Electron self-energy. - 2.4. Spin susceptibility and electrical resistivity. - 3. Effects of lattice fluctuation on CDW transition. - 3.1. Model. - 3.2. Calculated results for the 1D system. - 3.3. Calculated results for the 3D system. - 4. Effects of lattice fluctuations on the electronic density of states, spin susceptibility, and electrical resistivity. - 4.1. The 1D system. - 4.2. The 3D system. - 5. Supplementary remarks. - Appendix A. Feynman rules for ? and ? - Appendix B. Evaluation of frequency sum with the use of contour integral in the complex plane. - Phenomenological Landau Theory of Charge Density Wave Phase Transitions in Layered Compounds. - 1. Introduction. - 2. Construction of Landau free energy. - 2.1. 2H-TaSe2. - 2.2. 1T-TaS2 and TaSe2. - 3. A simple example: single-q CDW. - 3.1. Successive phase transitions and discommensurate state. - 3.2. Fluctuation modes. - 4. 2H-TaSe2. - 4.1. Basic features of phase transitions. - 4.2. Single-layer properties. - 4.3. Commensurate phases with various symmetries. - 4.4. Discommensuration structures of two-layer stacking. - 4.5. Reentrant lock-in transition caused by pressure. - 4.6. Discommensuration diagram and dislocations. - 4.7. Fluctuation modes. - 4.8. 2H-NbSe2. - 5. 1T-TaS2 and TaSe2. - 5.1. Brief summary of observed phase transitions. - 5.1. 1. 1T-TaS2. - 5.1. 2. 1T-TaSe2. - 5.2. Single-layer properties. - 5.2.1. Commensurate state. - 5.2.2. Incommensurate states and discommensuration structures. - 5.3. Three-dimensional orderings of charge density waves. - 5.3.1. Commensurate states. - 5.3.2. Incommensurate and discommensurate states. - 5.4. New phase of 1T-TaS2. - 6. Concluding remarks. - Charge Density Waves in the Transition-metal Dichalcogenides: Recent Experimental Advances. - 1. Introduction. - 2. Charge density wave transformations observed in the Group Vb compounds. - 2.1. 2H structures. - 2.2. 1T structures. - 3. The 2a0 superlattice in the Group IVb compound 1T-TiSe2. - 3.1. General features. - 3.2. Infrared reflectivity-free carrier and phonon effects. - 3.3. Phonon dispersion at low temperature. - 3.4. Angle-resolved photoemission and the electronic structure of TiSe2. - 3.5. The transformed band structure of TiSe2. - 4. Recent developments. - Index of Names. - Index of Subjects.