= XXZ spin chain
{c}
{title2=$H=J\sum_j(S_j^xS_{j+1}^x+S_j^yS_{j+1}^y+\Delta S_j^zS_{j+1}^z)$}
The <XXZ spin chain> has equal transverse <exchange interactions> and a possibly different longitudinal coupling. For $J>0$ the transverse coupling is antiferromagnetic, while the sign and size of $\Delta$ determine the longitudinal preference. A periodic even chain is bipartite. Its <continuous symmetry> is rotation about $z$ for generic $\Delta$, enhanced to full <spin> rotation at $\Delta=1$.
Back to article page
