Observation of the Fermi surface, the band structure, and their diffraction replicas ofSr14−xCaxCu24O41by angle-resolved photoemission spectroscopy

We have investigated the electronic structure of ${\text{Sr}}_{14\ensuremath{-}x}{\text{Ca}}_{x}{\text{Cu}}_{24}{\text{O}}_{41}$ $(x=0;\text{ }11.5)$ single crystals by angle-resolved photoemission spectroscopy. A satisfactory agreement with band-structure calculations is found. The Fermi surface is observed for ${\text{Sr}}_{2.5}{\text{Ca}}_{11.5}{\text{Cu}}_{24}{\text{O}}_{41}$ from which we derive a charge carrier concentration between 0.15 and 0.2 holes per Cu atom at $T=25\text{ }\text{K}$ in the ladder substructure. The chain substructures, on the other hand, act as diffraction grating for the ladder photoelectrons giving rise to incommensurate replicas of the ladder bands.