Samarakoon Anjana M, Grigera S A, Tennant D Alan, Kirste Alexander, Klemke Bastian, Strehlow Peter, Meissner Michael, Hallén Jonathan N, Jaubert Ludovic, Castelnovo Claudio, Moessner Roderich
Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831.
Shull Wollan Center-A Joint Institute for Neutron Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831.
Proc Natl Acad Sci U S A. 2022 Feb 1;119(5). doi: 10.1073/pnas.2117453119.
Noise generated by motion of charge and spin provides a unique window into materials at the atomic scale. From temperature of resistors to electrons breaking into fractional quasiparticles, "listening" to the noise spectrum is a powerful way to decode underlying dynamics. Here, we use ultrasensitive superconducting quantum interference device (SQUIDs) to probe the puzzling noise in a frustrated magnet, the spin-ice compound DyTiO (DTO), revealing cooperative and memory effects. DTO is a topological magnet in three dimensions-characterized by emergent magnetostatics and telltale fractionalized magnetic monopole quasiparticles-whose real-time dynamical properties have been an enigma from the very beginning. We show that DTO exhibits highly anomalous noise spectra, differing significantly from the expected Brownian noise of monopole random walks, in three qualitatively different regimes: equilibrium spin ice, a "frozen" regime extending to ultralow temperatures, and a high-temperature "anomalous" paramagnet. We present several distinct mechanisms that give rise to varied colored noise spectra. In addition, we identify the structure of the local spin-flip dynamics as a crucial ingredient for any modeling. Thus, the dynamics of spin ice reflects the interplay of local dynamics with emergent topological degrees of freedom and a frustration-generated imperfectly flat energy landscape, and as such, it points to intriguing cooperative and memory effects for a broad class of magnetic materials.
电荷和自旋运动产生的噪声为在原子尺度上研究材料提供了一个独特的窗口。从电阻器的温度到电子分裂成分数准粒子，“聆听”噪声谱是解码潜在动力学的有力方法。在这里，我们使用超灵敏超导量子干涉器件（SQUID）来探测受挫磁体——自旋冰化合物DyTiO（DTO）中令人困惑的噪声，揭示了协同效应和记忆效应。DTO是一种三维拓扑磁体，其特征是涌现出静磁学和典型的分数化磁单极准粒子，其实时动力学性质从一开始就是个谜。我们表明，DTO在三种性质不同的状态下表现出高度异常的噪声谱，与单极随机游走预期的布朗噪声有显著差异：平衡自旋冰、延伸至超低温的“冻结”状态以及高温“异常”顺磁体。我们提出了几种不同的机制，这些机制会产生不同颜色的噪声谱。此外，我们确定局部自旋翻转动力学的结构是任何建模的关键要素。因此，自旋冰的动力学反映了局部动力学与涌现的拓扑自由度以及受挫产生的不完全平坦能量景观之间的相互作用，因此，它指出了一类广泛磁性材料中有趣的协同效应和记忆效应。
