Atomic and electronic structure of domains walls in a polar metal

Polar metals counterintuitively bring two well-known phenomena into coexistence, namely, bulk polar displacements, and an electronic Fermi surface giving rise to metallic conduction. However, little is known about the polar domains or domain walls in such materials. Using atomic resolution electron microscopy imaging combined with first principles density functional theory, we show that uncharged head-to-tail walls, and "charged" head-to-head and tail-to-tail walls can exist in the bulk of such crystals of polar metals Ca3Ru2O7, where both structural changes at the wall as well as electrostatic considerations define the wall nature. Significant built-in potentials of 30-170 meV are predicted at such walls.