NUMERICAL STUDY OF THE INCOMMENSURATE PHASE IN SPIN-PEIERLS SYSTEMS

We analyze several properties of the lattice solitons in the incommens urate phase of spin-Peierls systems using exact diagonalization and qu antum Monte Carlo simulations. These systems are modeled by an antifer romagnetic Heisenberg chain with nearest-and next-nearest-neighbor int eractions coupled to the lattice in the adiabatic approximation. Sever al relations among features of the solitons and magnetic properties of the system have been determined and compared with analytical predicti ons. We have studied in particular the relation between the soliton wi dth and the spin-Peierls gap. Although this relation has the form pred icted by bosonized field theories, we have found some important quanti tative differences which could be relevant to describe experimental st udies of spin-Peierls materials.