Strong-coupling approach to the magnetization process of polymerized quantum spin chains

Polymerized quantum spin chains (i.e., spin chains with a periodic modulation of the coupling constants) exhibit plateaus in their magnetization curves when subjected to homogeneous external magnetic fields. We argue that the strong-coupling limit yields a simple but general explanation for the appearance of plateaus as well as of the associated quantization condition on the magnetization. We then proceed to explicitly compute series for the plateau boundaries of trimerized and quadrumerized spin-1/2 chains. The picture is completed by a discussion of how the universality classes associated with the transitions at the boundaries of magnetization plateaus arise in many cases from a first-order strong-coupling effective Hamiltonian.