二维海森堡自旋玻璃中的通量$1/f^α$噪声：弱各向异性相互作用的影响
Flux $1/f^α$ noise in 2D Heisenberg spin glasses: effects of weak anisotropic interactions
摘要：
研究了具有各向同性RKKY和较弱的各向异性偶极-偶极耦合的随机分布的经典海森堡自旋二维系综的动力学。这样的系综可能导致在具有$1/f^α$功率谱（$α\lesssim 1$）的SQUID中观察到的通量噪声。数值求解了无耗散极限下的Landau-Lifshiftz-Gilbert运动方程。我们发现，伊辛型涨落，这是由自旋聚集接近自旋玻璃临界行为与$T_c =0$，引起$1/f^α$噪声。即使是弱的各向异性相互作用也会导致从海森堡型临界性到更强的伊辛型临界性的交叉。温度依赖指数$α(T) \lesssim 1$在温度降低时增长并接近1。该机制与自旋扩散机制平行作用。而后者是敏感的设备的几何形状，自旋集群机制在很大程度上是几何形状无关的。
英文摘要：
We study the dynamics of a two-dimensional ensemble of randomly distributed classical Heisenberg spins with isotropic RKKY and weaker anisotropic dipole-dipole couplings. Such ensembles may give rise to the flux noise observed in SQUIDs with a $1/f^α$ power spectrum ($α\lesssim 1$). We solve numerically the Landau-Lifshiftz-Gilbert equations of motion in the dissipationless limit. We find that Ising type fluctuators, which arise from spin clustering close to a spin-glass critical behavior with $T_c =0$, give rise to $1/f^α$ noise. Even weak anisotropic interactions lead to a crossover from the Heisenberg-type criticality to the much stronger Ising-type criticality. The temperature dependent exponent $α(T) \lesssim 1$ grows and approaches unity when the temperature is lowered. This mechanism acts in parallel to the spin diffusion mechanism. Whereas the latter is sensitive to the device geometry, the spin-clustering mechanism is largely geometry independent.
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