Possible high-Tc superconductivity due to incipient narrow bands originating from hidden ladders in Ruddlesden-Popper compounds

We introduce the concept of "hidden ladders" for the bilayer Ruddlesden-Popper-type compounds: While the crystal structure is bilayer, d(xz) (d(yz)) orbitals in the relevant t(2g) sector of the transition metal form a two-leg ladder along x(y) since the d(xz) (d(yz)) electrons primarily hop in the leg (x, y) direction along with the rung (z) direction. This leads us to propose that Sr3Mo2O7 and Sr3Cr2O7 are candidates for the hidden-ladder material, with the correct position of E-F from a first-principles band calculation. Based on the analysis of Eliashberg equation, we predict the possible occurrence of high-temperature superconductivity in these noncopper materials arising from the interband pair-scattering processes between a wide band and an "incipient" narrow band on the ladder.