SU(4) Theory for Spin Systems with Orbital Degeneracy

The isotropic limit of spin systems with orbital degeneracy has global SU(4) symmetry. On many 2D lattices, the ground state does not possess long-range order, which may explain the observed spin liquid properties of LiNiO{sub 2} . In the SU(4) N{acute e}el-ordered state, spin-spin correlations can be antiferromagnetic between two neighboring sites with parallel magnetic moments. {copyright} {ital 1998} {ital The American Physical Society }