DOPING EFFECT ON SPIN-PEIERLS INSTABILITY

We study the effects of doping on spin-Peierls (SP) systems using the unimodular mean-field theory. The impurity spins affect the singlet valence bond field and renormalize the magnetic excitations. The SP transition temperature and the energy gap of magnetic excitations are reduced by factors similar to n(i) and similar to n(i)(2/3), respectively, with n(i) as the impurity density. At a certain value of n(i), a gapless SP phase occurs, and the interaction between impurities becomes RKKY-like. The recently observed reduction of SP transition temperature upon doping and occurrence of a spin glass phase is interpreted using the proposed theory.