Ferroelectricity in molecular solids: a review of electrodynamic properties

In conventional ferroelectrics the polarization is induced either by the relative displacement of positive and negative ions due to a lattice distortion or by the collective alignment of permanent electric dipoles. Strongly correlated materials with the inversion-symmetry-broken ground states feature electronic ferroelectricity, a phenomenon which has recently caught the attention of condensed matter physicists due to its great fundamental and technological importance. The discovery of electronic ferroelectricity in one and two-dimensional molecular solids is an exciting development because they show a rich variety of nonlinear properties and complex electrodynamics, including nontrivial emergent excitations. We summarize key experimental results, sketch the current theoretical understanding and outline promising prospects of this phenomenon which have great potential for future electronic devices.