Dynamic multiferroicity of a ferroelectric quantum critical point

TL;DR

This paper predicts that ferroelectric quantum critical points inherently exhibit multiferroic behavior, with enhanced magnetic responses due to entangled electric and magnetic fluctuations, exemplified by strontium titanate.

Contribution

It demonstrates that ferroelectric quantum critical points are naturally multiferroic, showing entangled electric and magnetic fluctuations and measurable magnetic susceptibility enhancements.

Findings

Magnetic susceptibility is enhanced near the FE QCP.

Entangled electric and magnetic fluctuations lead to observable magnetic moments.

Strontium titanate is a candidate material exhibiting these effects.

Abstract

Quantum matter hosts a large variety of phases, some coexisting, some competing; when two or more orders occur together, they are often entangled and cannot be separated. Dynamical multiferroicity, where fluctuations of electric dipoles lead to magnetisation, is an example where the two orders are impossible to disentangle. Here we demonstrate elevated magnetic response of a ferroelectric near the ferroelectric quantum critical point (FE QCP) since magnetic fluctuations are entangled with ferroelectric fluctuations. We thus suggest that any ferroelectric quantum critical point is an \textit{inherent} multiferroic quantum critical point. We calculate the magnetic susceptibility near the FE QCP and find a region with enhanced magnetic signatures that appears near the FE QCP, and controlled by the tuning parameter of the ferroelectric phase. The effect is small but observable - we propose quantum paraelectric strontium titanate as a candidate material where the magnitude of the induced magnetic moments can be $\sim 5 \times 10^{-7} \mu_{B}$ per unit cell near the FE QCP.