Ising-chain quantum critical point
= Ising-chain quantum critical point
{c}
{title2=$g_c=1$}
For positive ferromagnetic exchange and nonnegative transverse field, the <Ising-chain quasiparticle dispersion> closes its gap at $g=1$, with $\epsilon_k\sim2J|k|$. This is the <quantum phase transition> between the model's ordered and field-polarized regimes. The exact dispersion identifies the gapless scale; computing its order parameter additionally requires ground-state correlations.