Spinon excitation and Mobius boundary condition in S=1/2 antiferromagneticHeisenberg spin ladder with zigzag structure - art. no. 212406

We investigate the low-lying excitation of the antiferromagnetic zigzag spi n ladder with Mobius boundary condition. Using the Lanczos and Householder diagonalization methods, we calculate the excitation spectrum of the zigzag ladder in the momentum space. We then show that the topological defect gen erated by the Mobius boundary provides the clear evidence of the single-spi non excitation. On the basis of the obtained single-spinon dispersion curve , we analyze the two-spinon scattering states under the usual periodic boun dary condition. We further discuss the interaction effect between the spino ns, and the connection to the cusp singularity in the magnetization process .