Novel Ordered Phases in the Orthogonal Dimer Spin System SrCu_2(BO_3)_2
Novel Ordered Phases in the Orthogonal Dimer Spin System SrCu_2(BO_3)_2
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正交二聚体自旋系统SrCu_2(BO_3)_2中的新型有序相
DOI：
10.1143/jpsj.79.011005
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
and C.Berthier
中科院分区：
文献类型：
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作者：
M. Takigawa;T. Waki;M. Horvatic;and C.Berthier
对二维 (2D) Shastry-Sutherland 晶格上的模型自旋系统 SrCu2(BO3)2 的磁特性进行了回顾，特别强调了核磁共振 (NMR) 实验。 SrCu2(BO3)2在零磁场下具有二聚体单线态基态，在高磁场下显示出一系列磁化平台。平台归因于三重态由于相互排斥而定位在超晶格中。通过核磁共振实验，确实在1/8平台处观察到了这样的上层建筑。此外，上部结构持续高于 1/8 平台，扭矩和核磁共振测量已识别出新的相。 SrCu2(BO3)2还具有各向异性的Dzyaloshinski-Moriya相互作用，可显着改变磁场中的基态。最近的进展是发现了高压下新的磁相变。在 2.4 GPa 下，11B NMR 谱显示出谱线分裂随温度变化的两步变化。 30 K 以下的逐渐分裂表明四重对称性丧失，随后在 4 K 以下进一步突然分裂，标志着明显的磁相变。低 T 相具有双晶胞，但没有自发磁矩。提出了一种新型的价键固体（VBS）顺序。
The magnetic properties of SrCu2(BO3)2, a model spin system on the two-dimensional (2D) Shastry–Sutherland lattice, are reviewed with particular emphasis on the nuclear magnetic resonance (NMR) experiments. SrCu2(BO3)2has a dimer singlet ground state at zero magnetic field and shows a sequence of magnetization plateaux at high magnetic fields. The plateaux are attributed to the localization of triplets into a superlattice due to mutual repulsion. Such a superstructure has been indeed observed at the 1/8 plateau by NMR experiments. Furthermore, the superstructure persists above the 1/8 plateau, where new phases have been identified by the torque and NMR measurements. SrCu2(BO3)2also has the anisotropic Dzyaloshinski–Moriya interactions, which significantly change the ground state in magnetic fields. A recent development is the discovery of a new magnetic phase transition under high pressure. At 2.4 GPa, the11B NMR spectrum exhibits line splitting as a function of temperature in two steps. A gradual splitting below 30 K indicating loss of four-fold symmetry is followed by a further sudden splitting below 4 K marking a clear magnetic phase transition. The low-Tphase has a doubled unit cell, yet with no spontaneous magnetic moment. A new type of valence-bond-solid (VBS) order is proposed.