Long-range crystalline nature of the Skyrmion lattice in MnSi.

We report small angle neutron scattering of the Skyrmion lattice in MnSi using an experimental setup that minimizes the effects of demagnetizing fields and double scattering. Under these conditions, the Skyrmion lattice displays resolution-limited Gaussian rocking peaks that correspond to a magnetic correlation length in excess of several hundred micrometers. This is consistent with exceptionally well-defined long-range order. We further establish the existence of higher-order scattering, discriminating parasitic double scattering with Renninger scans. The field and temperature dependence of the higher-order scattering arises from an interference effect. It is characteristic for the long-range crystalline nature of the Skyrmion lattice as shown by simple mean-field calculations.