Valence-Bond Crystal, and Lattice Distortions in a Pyrochlore Antiferromagnet with Orbital Degeneracy
| dc.creator | Di Matteo, S. | |
| dc.creator | Jackeli, G. | |
| dc.creator | Perkins, N. B. | |
| dc.date | 2005-01-12 | |
| dc.date.accessioned | 2026-07-07T03:03:11Z | |
| dc.date.available | 2026-07-07T03:03:11Z | |
| dc.description | We discuss the ground state properties of a spin 1/2 magnetic ion with threefold $t_{2g}$ orbital degeneracy on a highly frustrated pyrochlore lattice, like Ti$^{3+}$ ion in B-spinel MgTi$_2$O$_4$. We formulate an effective spin-orbital Hamiltonian and study its low energy sector by constructing several exact-eigenstates in the limit of vanishing Hund's coupling. We find that orbital degrees of freedom modulate the spin-exchange energies, release the infinite spin-degeneracy of pyrochlore structure, and drive the system to a non-magnetic spin-singlet manifold. The latter is a collection of spin-singlet dimers and is, however, highly degenerate with respect of dimer orientations. This ``orientational'' degeneracy is then lifted by a magneto-elastic interaction that optimizes the previous energy gain by distorting the bonds in suitable directions and leading to a tetragonal phase. In this way a valence bond crystal state is formed, through the condensation of dimers along helical chains running around the tetragonal c-axis, as actually observed in MgTi$_2$O$_4$. The orbitally ordered pattern in the dimerized phase is predicted to be of ferro-type along the helices and of antiferro-type between them. Finally, through analytical considerations as well as numerical ab-initio simulations, we predict a possible experimental tool for the observation of such an orbital ordering, through resonant x-ray scattering. | |
| dc.description | 15 pages, 8 figures | |
| dc.identifier | https://arxiv.org/abs/cond-mat/0501289 | |
| dc.identifier | http://arxiv.org/abs/cond-mat/0501289 | |
| dc.identifier | Phys. Rev. B 72, 024431 (2005) | |
| dc.identifier | doi:10.1103/PhysRevB.72.024431 | |
| dc.identifier.uri | http://salesiana.dossiersoluciones.com/handle/123456789/25663 | |
| dc.subject | Strongly Correlated Electrons | |
| dc.title | Valence-Bond Crystal, and Lattice Distortions in a Pyrochlore Antiferromagnet with Orbital Degeneracy | |
| dc.type | text |