Can a charge-ordered state be metallic?

Abstract Charge order means that two or more distinct charge states accommodate at different atomic sites, resulting in striking variations in the structural and physical properties. Charge-ordered systems are usually electrically insulating. Here, we present the first observation of a charge-ordered metallic state in a CaFe0.95Co0.05O3 single crystal, doped with a small amount of Co, and grown at high pressure. A metal-to-insulator transition occurs on cooling to 260 K owing to the charge order between the disproportionated Fe3+ and Fe5+ states. As the temperature further decreases to 65 K, however, a reentrant metallization transition accompanied by a newly presented antiferromagnetic phase transition takes place, whereas the Fe3+ and Fe5+ charge-ordered state exists robustly. An unprecedented charge-ordered metallic state is thus unveiled to exist in the CaFe0.95Co0.05O3 single crystal. First-principles calculations suggest that the introduction of a moderate amount of Co and peculiar spiral spin texture play an important role in the existence of this novel quantum state. This study opens up a new avenue to study charge-ordered behavior in a metallic system.