Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 151-747, Korea and Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea.
Center for Strongly Correlated Materials Research, Seoul National University, Seoul 151-747, Korea and Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea.
Phys Rev Lett. 2013 Dec 20;111(25):257202. doi: 10.1103/PhysRevLett.111.257202. Epub 2013 Dec 18.
The breakdown of magnons, the quasiparticles of magnetic systems, has rarely been seen. By using an inelastic neutron scattering technique, we report the observation of spontaneous magnon decay in multiferroic LuMnO3, a simple two dimensional Heisenberg triangular lattice antiferromagnet, with large spin S=2. The origin of this rare phenomenon lies in the nonvanishing cubic interaction between magnons in the spin Hamiltonian arising from the noncollinear 120° spin structure. We observed all three key features of the nonlinear effects as theoretically predicted: a rotonlike minimum, a flat mode, and a linewidth broadening, in our inelastic neutron scattering measurements of single crystal LuMnO3. Our results show that quasiparticles in a system hitherto thought of as "classical" can indeed break down.
磁振子（磁系统的准粒子）的破裂很少被观察到。通过使用非弹性中子散射技术，我们报告了在多铁性 LuMnO3 中自发磁振子衰减的观察结果，LuMnO3 是一个简单的二维海森堡三角晶格反铁磁体，具有大自旋 S=2。这种罕见现象的起源在于自旋哈密顿量中磁子之间的非零立方相互作用，这是由非共线 120°自旋结构引起的。在对单晶 LuMnO3 的非弹性中子散射测量中，我们观察到了理论预测的所有三个非线性效应的关键特征：类轮式最小值、平带模式和线宽展宽。我们的结果表明，在一个迄今被认为是“经典”的系统中，准粒子确实可以破裂。
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