Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.
Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Phys Rev Lett. 2016 Feb 26;116(8):087201. doi: 10.1103/PhysRevLett.116.087201. Epub 2016 Feb 24.
We present single-crystal neutron scattering measurements of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba_{3}CoSb_{2}O_{9}. Besides confirming that the Co^{2+} magnetic moments lie in the ab plane for zero magnetic field and then determining all the exchange parameters of the minimal quasi-2D spin Hamiltonian, we provide conclusive experimental evidence of magnon decay through observation of intrinsic line broadening. Through detailed comparisons with the linear and nonlinear spin-wave theories, we also point out that the large-S approximation, which is conventionally employed to predict magnon decay in noncollinear magnets, is inadequate to explain our experimental observation. Thus, our results call for a new theoretical framework for describing excitation spectra in low-dimensional frustrated magnets under strong quantum effects.
我们呈现了对自旋为 1/2 的等边三角晶格反铁磁体 Ba3CoSb2O9 的单晶中子散射测量结果。除了证实 Co2+磁矩在零磁场下位于 ab 平面，然后确定最小准二维自旋哈密顿量的所有交换参数外，我们还通过观察固有线宽提供了磁子衰减的确凿实验证据。通过与线性和非线性自旋波理论的详细比较，我们还指出，在传统上用于预测非共线磁体中磁子衰减的大 S 近似，不足以解释我们的实验观察结果。因此，我们的结果呼吁为在强量子效应下描述低维受挫磁体的激发谱建立新的理论框架。
