In the spin-Peierls compound ${\mathrm{CuGeO}}_3$, the commensurate-incommensurate transition concerning the modulation of atomic position and the local spin polarization is fully monitored (at $T=4\mathrm{}\mathrm{K}$ $\simeq$ zero- $T$ limit) by the application of an external magnetic field $\left(H\right)$ above a threshold value $H_c\simeq 13\mathrm{T}$. The solitonic profile of the spin polarization, as well as its absolute magnitude, has been precisely imaged from ${}^{65}\mathrm{Cu}$ NMR line shapes obtained for $h=\left({H-H}_c\right)/H_c$ varying from 0.0015 to 1. This offers a unique possibility to test quantitatively the various numerical and analytical methods developed to solve a generic Hamiltonian in 1D physics, namely strongly interacting fermions in the presence of electron-phonon coupling at arbitrary band filling.

• Received 20 November 1998

DOI:https://doi.org/10.1103/PhysRevLett.83.420