Figure 1: Planar geometries of cuprate, titanium-oxypnictide, and iron-pnictide superconducting families.
From: Intra-unit-cell nematic charge order in the titanium-oxypnictide family of superconductors
(a–c) Planar motifs in cuprates, titanium oxypnictides and iron pnictides, respectively. Solid grey lines show the metal-anion square net, and dotted black lines show the square net of second-nearest-neighbour atoms. The + and −signs in b and c denote As atoms that are above and below the plane, respectively. (d) TiO2Pn4 octahedral motif found in BaTi2Pn2O. (e) Schematics of the Ti 3d-orbital energy levels for the two distinct Ti sites labelled in b, Ti(1) and Ti(2). The two lowest-lying orbitals marked in red form two bands occupied by one electron per Ti.
