Fragmented monopole crystal, dimer entropy and Coulomb interactions in Dy$_2$Ir$_2$O$_7$

TL;DR

This study demonstrates that Dy$_2$Ir$_2$O$_7$ hosts a fragmented monopole crystal state with coexisting magnetic order and spin liquid behavior, supported by neutron scattering and thermodynamic measurements, and modeled through Coulomb interactions.

Contribution

It provides a detailed experimental and theoretical analysis of the fragmented monopole crystal state in Dy$_2$Ir$_2$O$_7$, including thermodynamics, excitations, and domain wall effects.

Findings

Residual entropy matches a hard core dimer liquid

Coulomb interactions quantitatively explain thermodynamics and magnetization

Low energy excitations and broad energy barrier distribution observed

Abstract

Neutron scattering, specific heat and magnetisation measurements on both powders and single crystals reveal that Dy$_2$Ir$_2$O$_7$ realizes the fragmented monopole crystal state in which antiferromagnetic order and a Coulomb phase spin liquid co-inhabit. The measured residual entropy is that of a hard core dimer liquid, as predicted. Inclusion of Coulomb interactions allows for a quantitative description of both the thermodynamic data and the magnetisation dynamics, with the energy scale given by deconfined defects in the emergent ionic crystal. Our data reveal low energy excitations, as well as a large distribution of energy barriers down to low temperatures, while the magnetic response to an applied field suggests that domain wall pinning is important; results that call for further theoretical modelling.