J. Bonca et al., DIRECT CALCULATION OF SPIN STIFFNESS FOR SPIN-1 2 HEISENBERG MODELS/, Physical review. B, Condensed matter, 50(5), 1994, pp. 3415-3418
The spin stiffness of frustrated spin-1/2 Heisenberg models in one and
two dimensions is computed by exact diagonalizations on small cluster
s that implement spin-dependent twisted boundary conditions. Finite-si
ze extrapolation to the thermodynamic limit yields a value of 0.14 +/-
0.01 for the spin stiffness of the unfrustrated planar antiferromagne
t. We also present a general discussion of the linear-response theory
for spin twists, which ultimately leads to the moment sum rule.