Exact solution of the two-magnon problem in the $k=-\pi /2$ sector of a finite-size anisotropic spin-1/2 frustrated ferromagnetic chain

Zimeng Li, Ning Wu

The two-magnon problem in the $k=-\pi /2$ sector of a \emph{finite-size} spin-1/2 chain with ferromagnetic nearest-neighbor (NN) interaction $(J_1>0)$ and antiferromagnetic next-neare…