Spin gap in chains with hidden symmetries
Spin gap in chains with hidden symmetries
We investigate the formation of a spin gap in one-dimensional models characterized by groups with hidden dynamical symmetries. A family of two-parametric models of isotropic and anisotropic spin-rotator chains (SRC's) characterized by $\mathrm{SU}(2)\ifmmode\times\else\texttimes\fi{}\mathrm{SU}(2)$ and $\mathrm{SO}(2)\ifmmode\times\else\texttimes\fi{}\mathrm{SO}(2)\ifmmode\times\else\texttimes\fi{}{\mathrm{Z}}_{2}\ifmmode\times\else\texttimes\fi{}{\mathrm{Z}}_{2}$ symmetries is introduced to describe the transition from SU(2) to SO(4) antiferromagnetic Heisenberg chains. The …