Dynamically induced magnetism in KTaO$_3$

TL;DR

This paper demonstrates that circularly polarized laser pulses can induce measurable magnetic moments in paraelectric KTaO$_3$ through dynamical multiferroicity, revealing a new way to generate magnetism in non-magnetic materials.

Contribution

It identifies KTaO$_3$ as a candidate for dynamical multiferroicity and predicts laser-induced magnetic moments via soft phonon mode coupling, supported by ab initio calculations.

Findings

Laser pulses induce ~5% of nuclear magneton magnetic moments in KTaO$_3$

Soft phonon mode T$_{1u}$ couples to external field and induces magnetization

Electron magnetic effects are significantly enhanced due to mass difference

Abstract

Dynamical multiferroicity features entangled dynamic orders: fluctuating electric dipoles induce magnetization. Hence, the material with paraelectric fluctuations can develop magnetic signatures if dynamically driven. We identify the paraelectric KTaO$_3$ (KTO) as a prime candidate for the observation of the dynamical multiferroicity. We show that when a KTO sample is exposed to a circularly polarized laser pulse, the dynamically induced ionic magnetic moments are of the order of 5\% of the nuclear magneton per unit cell. We determine the phonon spectrum using ab initio methods and identify T$_{1u}$ as relevant soft phonon modes that couple to the external field and induce magnetic polarization. We also predict a corresponding electron effect for the dynamically induced magnetic moment which is enhanced by several orders of magnitude due to the significant mass difference between electron and ionic nucleus.