Ultrasonic elastic responses in a monopole lattice
Ultrasonic elastic responses in a monopole lattice
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DOI：
10.1088/1367-2630/aa6322
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发表时间：
2016-08
影响因子：
3.3
通讯作者：
Xiao-Xiao Zhang-Xiao;N. Nagaosa
中科院分区：
文献类型：
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作者：
Xiao-Xiao Zhang-Xiao;N. Nagaosa
最新的实验进展将手性磁体（MnSi/MnGe）中耦合力学自由度的场景扩展到拓扑非平凡的斯基子晶体甚至单极晶格。我们利用自旋波理论，提出了声子和磁振子的相互作用模型，以解释单极子晶格中具有拓扑相变的实验结果，即单极子-反单极子对的湮灭。我们再现了弹性模量的各向异性磁弹性调制：在相变周围的剧烈超声软化以及平行于磁场和正交于磁场的声波的多峰沟精细结构。实验结果表明，Dzyaloshinskii-Moriya相互作用引起的磁弹性耦合与交换相互作用引起的磁弹性耦合相当。还预测了其他可能性，如弹性硬化。研究表明，单极子缺陷及其运动在纳米锗中起着至关重要的作用。
The latest experimental advances have extended the scenario of coupling mechanical degrees of freedom in chiral magnets (MnSi/MnGe) to the topologically nontrivial skyrmion crystal and even monopole lattices. Equipped with a spin-wave theory highlighting the topological features, we devise an interacting model for acoustic phonons and magnons to explain the experimental findings in a monopole lattice with a topological phase transition, i.e. annihilation of monopole–antimonopole pairs. We reproduce the anisotropic magnetoelastic modulations of elastic moduli: drastic ultrasonic softening around the phase transition and a multi-peak-and-trench fine structure for sound waves parallel and orthogonal to the magnetic field, respectively. Comparison with experiments indicates that the magnetoelastic coupling induced by Dzyaloshinskii–Moriya interaction is comparable to that induced by the exchange interaction. Other possibilities such as elastic hardening are also predicted. The study implies that the monopole defects and their motion in MnGe play a crucial role.