Polar metals taxonomy for materials classification and discovery

Recent milestones in the synthesis and characterization of polar metals have contributed to a rapidly growing field of research, rich in materials physics and potential applications. The burgeoning interest, however, has been accompanied by varied and sometimes inconsistent terminology, inhibiting clear communication and revealing fundamental tensions between theoretical descriptions and microscopic materials models. The authors review the frontier of polar metals research from the perspectives of theory, experiment, and simulation, and introduce a uniform taxonomy for the classification of materials combining broken inversion symmetry and metallic conductivity. The authors use the framework to establish a new database of such materials and highlight opportunities for the discovery of novel polar metals.