Topological Sector Fluctuations and Curie Law Crossover in Spin Ice

TL;DR

This paper investigates the crossover between two Curie laws in spin ice, revealing how topological constraints influence magnetic susceptibility and providing a new local probe for topological sector fluctuations.

Contribution

It demonstrates the existence of two Curie laws in spin ice and links susceptibility measurements to topological sector fluctuations, supported by experiments and theory.

Findings

Observation of a crossover between high and low temperature Curie laws.

Excellent agreement between neutron scattering data and theoretical models.

Susceptibility at finite wave vector probes topological sector fluctuations.

Abstract

At low temperatures, a spin ice enters a Coulomb phase - a state with algebraic correlations and topologically constrained spin configurations. In Ho2Ti2O7, we have observed experimentally that this process is accompanied by a non-standard temperature evolution of the wave vector dependent magnetic susceptibility, as measured by neutron scattering. Analytical and numerical approaches reveal signatures of a crossover between two Curie laws, one characterizing the high temperature paramagnetic regime, and the other the low temperature topologically constrained regime, which we call the spin liquid Curie law. The theory is shown to be in excellent agreement with neutron scattering experiments. On a more general footing, i) the existence of two Curie laws appears to be a general property of the emergent gauge field for a classical spin liquid, and ii) sheds light on the experimental difficulty of measuring a precise Curie-Weiss temperature in frustrated materials; iii) the mapping between gauge and spin degrees of freedom means that the susceptibility at finite wave vector can be used as a local probe of fluctuations among topological sectors.