Dielectric relaxation by quantum critical magnons

TL;DR

This study experimentally observes dielectric relaxation caused by quantum critical magnons, revealing the interplay between spin and lattice excitations near a magnetic quantum critical point, indicating quantum multiferroic behavior.

Contribution

It provides the first experimental evidence of dielectric relaxation driven by quantum critical magnons and links magnetic excitations to electrical properties.

Findings

Activation energy softens near the quantum critical point.

Relaxation time follows single-magnon energy for H > H_c.

Electrical activity of coupled spin and lattice excitations demonstrated.

Abstract

We report the experimental observation of dielectric relaxation by quantum critical magnons. Complex capacitance measurements reveal a dissipative feature with a temperature-dependent amplitude due to low-energy lattice excitations and an activation behavior of the relaxation time. The activation energy softens close to a field-tuned magnetic quantum critical point at $H=H_c$ and follows single-magnon energy for $H>H_c$, showing its magnetic origin. Our study demonstrates the electrical activity of coupled low-energy spin and lattice excitations, an example of quantum multiferroic behavior.