Dynamic susceptibility and dynamic correlations in spin ice

TL;DR

This paper models the dynamic susceptibility and correlations in spin ice using emergent magnetic monopoles, revealing temperature-dependent behaviors and corrections to classical theories through a non-equilibrium thermodynamics approach.

Contribution

It introduces a novel application of non-equilibrium thermodynamics to spin ice, calculating dynamic responses and refining the understanding of magnetic monopole interactions.

Findings

At zero temperature, the correlation function matches static spin ice correlations.

Non-zero temperatures introduce a longitudinal component decreasing with temperature.

The model predicts different relaxation times for transverse and longitudinal monopole correlations.

Abstract

Here we calculate the dynamic susceptibility and dynamic correlation function in spin ice using the model of emergent magnetic monopoles. Calculations are based on a method originally suggested for the description of dynamic processes in water ice (non-equilibrium thermodynamics approach). We show that for zero temperature the dynamic correlation function reproduces the transverse dipole correlations (static correlation function) characteristic of spin ice in its ground state. At non-zero temperatures the dynamic correlation function includes an additional longitudinal component which decreases as the temperature decreases. Both terms (transverse and longitudinal) exhibit identical Debye-like dependences on frequency but with different relaxation times: the magnetic Coulomb interaction of monopoles reduces the longitudinal relaxation time with respect to the transverse one. We calculate the dielectric function for the magnetic monopole gas and discuss how the non-equilibrium thermodynamics approach exposes corrections to the Debye-Huckel theory of magnetic monopoles and the concept of "entropic charge".