Theory of spin density profile in the magnetization plateaus of SrCu₂(BO₃)₂

The two-dimensional spin-gap system ${\rm SrCu_2(BO_3)_2}$ shows unique physical properties due to the low-dimensionality character and the strong quantum fluctuations. Experimentally, 1/8-, 1/4-, and 1/3-plateaus have been observed in the magnetization curve under magnetic fields up to 70 Tesla, and the 1/2-plateau is expected to be stabilized at higher magnetic fields. We argue that spin-lattice effects are necessary to describe the superstructures at the plateaus, and we propose a simple microscopic model of spins interacting adiabatically with the lattice to reproduce the main features of the recent experimental results by nuclear magnetic resonance.