Angle-resolved photoemission measurements have been performed on ${\mathrm{Sr}}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ which consists of two-leg ${\mathrm{Cu}}_2{\mathrm{O}}_3$ ladders and edge-sharing ${\mathrm{CuO}}_2$ 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 $ka=(2n+1)\mathrm{}\pi /2,$ suggesting that a Mott-Hubbard gap opens on the ladder. The experimental result shows a qualitative agreement with the $t-J$ ladder calculation. It was also found that replacement of Sr with Ca causes a transfer of holes from the chain to the ladder.

• Received 19 May 1997

DOI:https://doi.org/10.1103/PhysRevB.56.7870