Fascinating materials: Polar metals

Polar metals are a unique class of materials that defies the traditional understanding of the relationship between polarization and electrical conductivity. Typically, polar materials possess broken inversion symmetry, resulting in an internal electric polarization, and are generally insulators. A notable subset of these materials is ferroelectric, where the electric polarization can be reversed by applying an external electric field. On the other hand, metals are expected to screen internal electric fields because of free electrons. However, polar metals challenge this view by combining metallic conductivity with a polar structure, where broken inversion symmetry exists even in the presence of free charge carriers. This combination allows for unusual and intriguing physical behaviors that could have significant implications for novel electronic and magnetic applications. Here, we will highlight the importance of recent discoveries in polar metals and their potential scientific and technological impacts, provided current challenges are overcome.