The spin ice compound Dy_2Ti_2O_7 stands out as the first topological magnet in three dimensions, with its tell-tale emergent fractionalized magnetic monopole excitations. Its real-time dynamical properties have been an enigma from the very beginning. Using ultrasensitive, non-invasive SQUID measurements, we show that Dy_2Ti_2O_7 exhibits a highly anomalous noise spectrum, in three qualitatively different regimes: equilibrium spin ice, a `frozen' regime extending to ultra-low temperatures, as well as a high-temperature `anomalous' paramagnet. We show that in the simplest model of spin ice, the dynamics is not anomalous, and we present several distinct mechanisms which give rise to a coloured noise spectrum. In addition, we identify the structure of the single-ion dynamics as a crucial ingredient for any modelling. Thus, the dynamics of spin ice Dy_2Ti_2O_7 reflects the interplay of local dynamics with emergent topological degrees of freedom and a frustration-generated imperfectly flat energy landscape, and as such should be relevant for a broad class of magnetic materials.
@article{arxiv.2107.11379,
title = {Anomalous magnetic noise in imperfect flat bands in the topological magnet Dy2Ti2O7},
author = {Anjana M. Samarakoon and S. A. Grigera and D. Alan Tennant and Alexander Kirste and Bastian Klemke and Peter Strehlow and Michael Meissner and Jonathan N. Hallen and Ludovic Jaubert and Claudio Castelnovo and Roderich Moessner},
journal= {arXiv preprint arXiv:2107.11379},
year = {2024}
}