Small parameter for Migdal-type description of t-t'-J model

The small parameter, validating Migdal's approximation for the spin-charge coupling vertex in the two-dimensional t-t'-J model close to half-filling, is found to be 1/ln(t/J), t>>J. An effective spin-charge separation, in the vicinity of the Fermi-level, reduces to zero the quasi-particle weight of electron states a half-filling. The calculated optical conductivity σ(ω) exhibits an open-quotes infraredclose quotes 1/ω tail with superimposed, multimagnon resonances