orbital_topics

Three main questions related to the physics of orbital degrees of freedom came to the fore in the discussion of Wednesday (biased view --JvdB).

We know that orbitals can order and that they couple to the lattice, but the questions are: 1. is there any material in which the //quantum// character of orbital degrees of freedom become relevant? 2. are there any cases where orbital //fluctuations//, either quantum or classical are relevent? 3. does orbital ordering have interesting //textures//, //symmetries// and/or //excitations//?

Also 15 more or less detailed discussion topics came up: 1. What is the role of vibronic coupling in cooperative Jahn-Teller systems 2. The importance of relativistic spin orbit coupling in eg and t2g systems 3. Orbital and frustration: frustration due to orbital degrees of freedom --- orbitals in frustrated lattices 4. Relative importance of electron-lattice effects (Jahn Teller) versus electronic effects (superexchange). 5. Role of geometry: differences for the situation of 180 degree O-TM-O bonds, 90 degree O-TM-O bonds and edge sharing octahedra 6. Reduced dimensionality due to orbitals 7. Importance of direct d-d electronic hopping versus d-oxygen-d hopping, especially in t2g spinels 8. Orbitals in charge transfer insulators 9. Role of orbital degrees of freedom at metal-insulator transitions 10. Orbital liquids -- quantum effects 11. Orbital waves -- orbitons 12. Importance of long-range interactions in short-range orbital (cooperative Jahn Teller) models 13. Multiplets en Mottiplets 14. Orbital textures, orbital domains and their effect on electronic degrees of freedom 15. What happens to orbital order when going to metallic states --orbital melting