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.

Valence-bond states in dynamical Jahn-Teller molecular system / Santoro, Giuseppe E.; Guidoni, L.; Parola, A.; Tosatti, E.. - In: PHYSICAL REVIEW. B, CONDENSED MATTER. - ISSN 0163-1829. - 55:24(1997), pp. 16168-16175. [10.1103/PhysRevB.55.16168]

Valence-bond states in dynamical Jahn-Teller molecular system

Santoro, Giuseppe E.;Tosatti, E.
1997-01-01

Abstract

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.
1997
55
24
16168
16175
https://arxiv.org/pdf/cond-mat/9809017.pdf
Santoro, Giuseppe E.; Guidoni, L.; Parola, A.; Tosatti, E.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11767/12558
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