Microscopic mechanism for the 1/8 magnetization plateau in SrCu_2(BO_3)_2

Abstract

The frustrated quantum magnet SrCu_2(BO_3)_2 shows a remarkably rich phase diagram in an external magnetic field including a sequence of magnetization plateaux. The by far experimentally most studied and most prominent magnetization plateau is the 1/8 plateau. Theoretically, one expects that this material is well described by the Shastry-Sutherland model. But recent microscopic calculations indicate that the 1/8 plateau is energetically not favored. Here we report on a very simple microscopic mechanism which naturally leads to a 1/8 plateau for realistic values of the magnetic exchange constants. We show that the 1/8 plateau with a diamond unit cell benefits most compared to other plateau structures from quantum fluctuations which to a large part are induced by Dzyaloshinskii-Moriya interactions. Physically, such couplings result in kinetic terms in an effective hardcore boson description leading to a renormalization of the energy of the different plateaux structures which we treat in this work on the mean-field level. The stability of the resulting plateaux are discussed. Furthermore, our results indicate a series of stripe structures above 1/8 and a stable magnetization plateau at 1/6. Most qualitative aspects of our microscopic theory agree well with a recently formulated phenomenological theory for the experimental data of SrCu_2(BO_3)_2. Interestingly, our calculations point to a rather large ratio of the magnetic couplings in the Shastry-Sutherland model such that non-perturbative effects become essential for the understanding of the frustrated quantum magnet SrCu_2(BO_3)_2.

24 pages, 24 figures

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• Crystals of bound states in the magnetization plateaus of the Shastry-Sutherland model
• Incomplete devil's staircase in the magnetization curve of SrCu2(BO3)2
• Magnetic chern bands and triplon Hall effect in an extended Shastry-Sutherland model
• Dynamics and Instabilities of the Shastry-Sutherland Model
• Tensor network study of the $m=1/2$ magnetization plateau in the Shastry-Sutherland model at finite temperature
• Degeneracy of the 1/8 plateau and antiferromagnetic phases in the Shastry-Sutherland magnet TmB4
• Nuclear Magnetic Resonance in High Magnetic Field: Application to Condensed Matter Physics
• Exotic magnetisation plateaus in a quasi-2D Shastry-Sutherland model
• Emergent Bound States and Impurity Pairs in Chemically Doped Shastry-Sutherland System
• Pressure dependence of the magnetization plateaus of SrCu_2(BO_3)_2
• Fractional magnetization plateaux of a spin-1/2 Heisenberg model on the Shastry-Sutherland lattice: effect of quantum XY interdimer coupling
• Magnetization plateaus and bipartite entanglement of an exactly solved spin-1/2 Ising-Heisenberg orthogonal-dimer chain
• Effects of staggered Dzyaloshinskii-Moriya interactions in a quasi-two-dimensional Shastry-Sutherland model
• Neural Network Quantum States analysis of the Shastry-Sutherland model