| After a brief review of the basic mechanisms for the formation of magnetization plateaux in frustrated quantum magnets, I will discuss the properties of SrCu2(BO3)2, the first compound in which high field measurements (up to 70 T) have revealed the presence of magnetization plateaux at 1/8, 1/4 and 1/3 of the saturation value. While it is well accepted that the origin of the plateaux is related to the special geometry of the compound, a 2D arrangement of orthogonal dimers known as the Shastry-Sutherland model, several issues remain open or controversial, in particular i) the actual plateau sequence of SrCu2(BO3)2, with conflicting results from recent torque and NMR measurements, ii) the nature of the phases between the plateaux (supersolid?), and iii) the magnetization plateaux of the Shastry-Sutherland model. In this talk, I will present the results of a recent investigation of the magnetization plateaux in the Shastry-Sutherland model using high-order degenerate perturbation theory based on a Continuous Unitary Transformation, with the surprising outcome that the series 1/9, 2/15, 1/6, 2/9, 1/3 and 1/2 seems to be stabilized. I will then show that these findings are in several respects in agreement with the latest NMR data, and I will discuss which extensions of the model might be necessary to close the remaining gap between theory and experiment. |
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