Greg Stone,1 Danilo Puggioni,2 Shiming Lei,1 Mingqiang Gu,2 Ke Wang,1 Yu Wang,3 Jianjian Ge,3 Xue-Zeng Lu,2 Zhiqiang Mao,1 James M. Rondinelli,2 and Venkatraman Gopalan,1 1Pennsylvania State University, 2Northwestern University, 3Tulane University
DMR-1420620 (primary), ARO W911NF-15-1-0017, DOE DE-SC0012375, DE-SC0012432
Polar metals counterintuitively bring two well-known phenomena into coexistence: bulk polar displacements and an electronic Fermi surface giving rise to metallic conduction. Little is known about the polar domains or domain walls in such materials. Using electron microscopy imaging and first-principles density functional theory, the MRSEC team showed that uncharged head-to-tail walls, and “charged” head-to-head and tail-to-tail walls can exist in crystals of polar metals Ca3Ru2O7. A significant change occurs in the local density of states occurs at these walls; the H-H and T-T 90 degree domain walls iexhibit distinct electrostatic profiles with a screening length of ~1 nm and a potential variation of 30 meV to 170 meV. Note that a typical silicon-based transistor requires 60 meV/decade to switch between the on and the off states. We surmise that such significant built-in potential could potentially be of use as a variable work function gate material and in interface-space charge mediated devices, such as memristors.
Physical Review B, 99, 014105 (2019) doi.org/10.1103/PhysRevB.99.014105