Dielectric relaxation in the quantum multiferroics Rb$_2$Cu$_2$Mo$_3$O$_{12}$ and Cs$_2$Cu$_2$Mo$_3$O$_{12}$

TL;DR

This study investigates dielectric relaxation phenomena in quantum multiferroic compounds Cs$_2$Cu$_2$Mo$_3$O$_{12}$ and Rb$_2$Cu$_2$Mo$_3$O$_{12}$, revealing how quantum critical magnons influence dielectric properties and identifying anomalies at specific temperatures.

Contribution

It provides a comparative analysis of dielectric responses in two related quantum multiferroics, highlighting the role of quantum critical magnons and dielectric relaxation anomalies.

Findings

Dielectric relaxation observed in both compounds near quantum critical points.

Dielectric relaxation in Cs$_2$Cu$_2$Mo$_3$O$_{12}$ is unaffected by magnon Bose-Einstein condensation.

Anomalies at 19 K in Rb$_2$Cu$_2$Mo$_3$O$_{12}$ suggest microscopic differences in dielectric activity.

Abstract

Motivated by the recent discovery of dielectric relaxation by quantum critical magnons in Cs$_2$Cu$_2$Mo$_3$O$_{12}$, we conduct a detailed analysis of its dielectric response and compare it to that in the isostructural compound Rb$_2$Cu$_2$Mo$_3$O$_{12}$. Measurements in the vicinity of the field-induced magnon softening show that its description in terms of 3D Bose-Einstein condensation of magnons quantum critical point is unaltered by the presence of dielectric relaxation. We also demonstrate the existence of dielectric relaxation anomalies at 19 K in Rb$_2$Cu$_2$Mo$_3$O$_{12}$ and discuss the implications for the microscopic origin of dielectric activity in two compounds.