Breaking symmetry with light: Ultrafast ferroelectricity and magnetism from three-phonon coupling

Abstract

A theory describing how ferroic properties can emerge transiently in the ultrafast regime by breaking symmetry with light through three-phonon coupling is presented. Particular emphasis is placed on the special case when two exactly degenerate midinfrared or THz phonons are resonantly pumped, since this situation can give rise to an exactly rectified ferroic response with damping envelopes of $\sim 1$ ps or less. Light-induced ferroelectricity and ferromagnetism are discussed in this context and a number of candidate materials that could display these phenomena are proposed. The same analysis is also applied to the interpretation of previous femtomagnetism experiments, performed in different frequency ranges (visible and near infrared), but sharing similar symmetry characteristics.