Raman resonance in spin S two-leg ladder systems

We argue that the Raman intensity in a spin S two-leg spin-ladder has a pseudo-resonance peak, whose width is very small at large S. The pseudo-resonance originates from the existence of a local minimum in the magnon excitation spectrum, and is located slightly below twice the magnon energy at the minimum. The physics behind the peak is similar to the excitonic scenario for the neutron and Raman resonances in a d-wave superconductor.