Soliton lattices in the incommensurate spin-Peierls phase: Local distortions and magnetizations

It is shown that nonadiabatic fluctuations of the soliton lattice in the spin-Peierls system ${\mathrm{CuGeO}}_3$ lead to an important reduction of the NMR line widths. These fluctuations are the zero-point motion of the massless phasonic excitations. Furthermore, we show that the discrepancy of x-ray and NMR soliton widths can be understood as the difference between a distortive and a magnetic width. Their ratio is controlled by the frustration of the spin system. By this work, theoretical and experimental results can be reconciled in two important points.