Analytic approach to the one-dimensional spin-Peierls system in the   entire frequency range
  We use the two cut-off renormalization group (RG) method to study the spin-Peierls model in one-dimension for the entire phonon frequency range. We integrate out the phonon and solve the effective Fermion system via mean field and RG methods. We make use of the symmetry that the Neel, dimerization, and spin current order parameters form an SU(2) triplet based on resolving the Fermion into left and right movers. We present the phase diagram and discuss its implications for the organic charge-transfer salt (TMTTF)$_2$PF$_6$. 
Ping Sun, D. Schmeltzer, A.R. Bishop