Pressure evolution of the Shastry-Sutherland magnet SrCu2(BO3)2

We investigate the evolution of crystal structure and individual magnetic couplings in the spin1/2 Shastry-Sutherland magnet SrCu2(BO3)2 under hydrostatic pressure. Our results based on ab initio electronic structure calculations suggest the highly anisotropic compressibility of the structure that strongly shrinks along the interlayer c direction, while only weakly changing in the ab plane. This leads to a moderate change in the intralayer exchange couplings J and J' within the Cu2O6 dimers and between the dimers, respectively. Above 4.5 GPa, SrCu2(BO3)2 transforms into a monoclinic phase that has been scarcely characterized experimentally. We propose an improved structural model of this phase, and identify its spin system as an anisotropic Shastry-Sutherland lattice featuring inequivalent interdimer couplings J1' and J2. Our results compare well to the available experimental data, and call for a further investigation of the spin-lattice coupling phenomena in SrCu2(BO3)2.