NMR of the Shastry-Sutherland lattice SrCu₂(BO₃)₂

SrCu₂(BO₃)₂ is a prominent realization of the Shastry-Sutherland lattice model [1]. In this quasi-two-dimensional compound, Cu²⁺ ions form orthogonal spin-singlet dimers with strong geometrical frustration of the next-nearest and nearest neighbor exchange interactions. SrCu₂(BO₃)₂ has been studied extensively using a variety of techniques, such as nuclear magnetic resonance (NMR) spectroscopy, or recent magnetization measurements up to 118 T. These experiments reveal a complex sequence of magnetization plateaus with differing commensurate magnetic superstructure, stemming from a stripe type order of triplet states [2-4]. Due to its highly sensitive local probe character, NMR can provide deep insight into the spin-coupling mechanisms and excitations at highest magnetic fields. We present ¹¹B NMR spectra measured in pulsed magnetic fields up to 56 T, and compare those with prior results obtained in highest static magnetic fields. Herewith, we prove the feasibility and efficacy of this new technique, yielding the capability for extended studies at highest magnetic fields up to the 100 T regime that determine the spin structure in the 1/3 magnetization plateau and beyond.