Anomalous magnetic noise in an imperfectly flat landscape in the topological magnet Dy <sub>2</sub> Ti <sub>2</sub> O <sub>7</sub>
Anjana Samarakoon, S. A. Grigera, D. M. Tennant, A. Kirste, Bastian Klemke, Peter Strehlow, Michael Meißner, Jonathan N. Hallén, Ludovic D. C. Jaubert, Claudio Castelnovo, Roderich Moessner
Abstract
(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.