We discuss a hopping model of electrons between idealized molecular sites with a local orbital degeneracy and a dynamical Jahn-Teller effect, for crystal field environments of sufficiently high symmetry. For the Mott-insulating case (one electron per site and large Coulomb repulsions), in the simplest twofold degenerate situation, we are led to consider a particular exchange Hamiltonian, describing two isotropic spin-1/2 Heisenberg problems coupled by a quartic term on equivalent bonds. This twin-exchange Hamiltonian applies to a physical regime in which the interorbital singlet is the lowest-energy intermediate state available for hopping. This regime is favored by a relatively strong electron-phonon coupling. Using variational arguments, a large-n limit, and exact diagonalization data, we find that the ground state, in the one dimensional case, is a solid valence-bond state. The situation in the two dimensional case is less clear. Finally, the behavior of the system up on hole doping is studied in one dimension.
|Titolo:||Valence-bond states in dynamical Jahn-Teller molecular system|
|Autori:||Giuseppe E. Santoro; L. Guidoni; A. Parola; E. Tosatti|
|Rivista:||PHYSICAL REVIEW. B, CONDENSED MATTER|
|Data di pubblicazione:||1997|
|Digital Object Identifier (DOI):||10.1103/PhysRevB.55.16168|
|Appare nelle tipologie:||1.1 Journal article|