Multiferroic-like Quasiparticles in Ferroelectrics

Multiferroics are materials with coexisting electric and magnetic orders that are of central importance for fundamental research and technological applications. Unfortunately, intrinsic multiferroics that operate at room temperature remain rare due to an apparent incompatibility between magnetism and ferroelectricity. Here we predict that pure ferroelectrics may support multiferroic-like quasiparticles, termed "multiferrons," that simultaneously carry static magnetic and electric dipoles. The electric dipole moment emerges from the parity-odd anharmonicity of the ferroelectric dynamics, while the magnetic moment has both paramagnetic and diamagnetic origins generated by circularly polarized transverse fluctuations of the ferroelectric polarization. In contrast to the established "dynamical multiferroicity" of circularly polarized phonons, which involves only oscillating electric dipoles, multiferrons exhibit or cause, apart from Zeeman and Einstein-de Haas effects, a linear dc Stark response, giant electric-field-tunable second-harmonic generation in the THz-frequency regime, and a magnetoelectric cross coupling. Multiferrons open a new route toward nonlinear THz optical applications and offer multiferroic functionalities with simple ferroelectrics.