Angle-resolved photoemission study of the ladder compound

Angle-resolved photoemission measurements have been performed on (Formula presented) which consists of two-leg (Formula presented) ladders and edge-sharing (Formula presented) chains. The data are consistent with the existence of a dispersive band near the Fermi level which has the periodicity of the ladder sublattice. The band shows a minimum binding energy at (Formula presented) suggesting that a Mott-Hubbard gap opens on the ladder. The experimental result shows a qualitative agreement with the (Formula presented) ladder calculation. It was also found that replacement of Sr with Ca causes a transfer of holes from the chain to the ladder.