A. Fledderjohann et al., CRITICAL PROPERTIES OF THE ONE-DIMENSIONAL SPIN-1 2 ANTIFERROMAGNETICHEISENBERG-MODEL IN THE PRESENCE OF A UNIFORM-FIELD/, Physical review. B, Condensed matter, 54(10), 1996, pp. 7168-7176
In the presence of a uniform field the one-dimensional spin-1/2 antife
rromagnetic Heisenberg model develops zero frequency excitations at fi
eld-dependent ''soft-mode'' momenta. We determine three types of criti
cal quantities, which we extract from the finite-size dependence of th
e lowest excitation energies, the singularities in the static structur
e factors and the infrared singularities in the dynamical structure fa
ctors at the soft mode momenta. We also compare our results with the p
redictions of conformal field theory.