Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Miyagi 980-8577, Japan.
Neutron Science Laboratory, Institute for Solid State Physics, University of Tokyo, Tokai, Ibaraki 319-1106, Japan.
Phys Rev Lett. 2015 Sep 18;115(12):127202. doi: 10.1103/PhysRevLett.115.127202. Epub 2015 Sep 15.
The temporal magnetic correlations of the triangular-lattice antiferromagnet NiGa_{2}S_{4} are examined through 13 decades (10^{-13}-1 sec) using ultrahigh-resolution inelastic neutron scattering, muon spin relaxation, and ac and nonlinear susceptibility measurements. Unlike the short-ranged spatial correlations, the temperature dependence of the temporal correlations show distinct anomalies. The spin fluctuation rate decreases precipitously upon cooling towards T^{}=8.5 K, but fluctuations on the microsecond time scale then persist in an anomalous dynamical regime for 4 K<T≤T^{}. As this time scale exceeds that of single-site dynamics by 6 orders of magnitude, these fluctuations bear evidence of emergent degrees of freedom within the short-range correlated incommensurate state of NiGa_{2}S_{4}.
通过使用超高分辨率非弹性中子散射、μ 子自旋弛豫以及交流和非线性磁化率测量，研究了三角晶格反铁磁体 NiGa_2S_4 的时间磁关联。与短程空间关联不同，时间关联的温度依赖性显示出明显的异常。自旋涨落率在冷却至 T^*=8.5 K 时急剧下降，但在 4 K<T≤T^*的异常动力学范围内，微秒时间尺度上的涨落仍然存在。由于这个时间尺度比单原子动力学的量级大 6 个数量级，这些涨落证明了 NiGa_2S_4 的短程关联的非晶态中出现了新的自由度。
