Frédéric Mila: The saga of the Shastry-Sutherland compound SrCu2(BO3)2

Since the discovery of its first magnetization plateaus in 1999, the Shastry-Sutherland compound SrCu2(BO3)2 has been the subject of intensive investigation, and its properties have challenged theorists since then. At ambient pressure, its improbable sequence of plateaus at 1/8, 2/15,1/6, 1/4, 1/3, 2/5 and 1/2 has resisted for 15 years until a plausible explanation in terms of a crystal of spin-2 bound states based on tensor-network calculations was put forward. Under pressure, two phase transitions have been observed in zero field, and the nature of both the intermediate phase and the phase transition to the Néel phase are still debated. Combining pressure and high field has revealed a wealth of new phases, including a 1/5 plateau of a new type and several spin supersolids. Finally, the nature of the gap closing has been investigated with inelastic neutron scattering up to 25.9 Tesla, and Matrix Product State simulations of the dynamical structure have helped interpreting it as a Bose-Einstein condensation of spin-2 bound states into a spin-nematic phase.