Origin of the second coherent peak in the dynamical structure factor of an asymmetric spin-ladder

Appearance of the second coherent peak in the dynamical structure factor of an asymmetric spin ladder is suggested. The general arguments are confirmed by the first order (with respect to the asymmetry) calculation for a spin ladder with singlet-rung ground state. Basing on this result a new interpretation is proposed for the inelastic neutron scattering data in the spin gap compound CuHpCl.