Can someone explain why a material that is supposed to be conductive imply?

(PhysOrg.com) -- The transition-metal monoxide FeO is an archetypal example of a Mott insulator—a material that should conduct electricity under conventional band theories but becomes an insulator when measured, especially at low temperatures—and a major iron-bearing component of the Earth’s interior. Understanding the high-pressure behavior of this material is important for both solid-state physics and Earth science. But despite considerable study over the past 30 years, the origin of the well-known high-pressure-induced cubic-rhombohedral ferroic transition in FeO, which is a distortion of the original cubic structure to that of as rhomboid shape, has been not well understood.