Anomalous magnetic noise in imperfect flat bands in the topological magnet Dy2Ti2O7

TL;DR

This study reveals highly anomalous magnetic noise in Dy2Ti2O7 across various regimes, highlighting complex dynamics involving topological excitations and local interactions, which challenge simple models of spin ice behavior.

Contribution

It demonstrates the presence of anomalous noise spectra in Dy2Ti2O7 and identifies key mechanisms and single-ion dynamics crucial for understanding its complex magnetic behavior.

Findings

Anomalous noise spectrum observed in three regimes: equilibrium, frozen, and high-temperature paramagnet.

Simple spin ice models do not reproduce the observed anomalous dynamics.

Single-ion dynamics and local interactions are essential for accurate modeling.

Abstract

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.