The color of magnetic monopole noise

Abstract

We relate the anomaly in the noise color of spin ice to the emergent nature of its magnetic monopoles and their non-trivial random walk. Monopoles are quasi-particles, and the spin vacuum in which they wander is not structureless. Rather, the underlying spin ensemble filters the thermal white noise, leading to non-trivial coevolution. Thus, monopoles can be considered as “dressed” random walkers, activated by a non-trivial stochastic force that subsumes mutual interactions and the coevolution of their spin vacuum. From this, we suggest that recent experimental results are interpretable in terms of monopole subdiffusion. We then conjecture relations between the color of the noise and other observables, such as relaxation time, monopole density, the dynamic exponent, and the order of the annihilation reaction, which suggests to us the introduction of spin-ice–specific critical exponents in a neighborhood of the ice manifold criticality.