We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) of ladder compounds Sr14-xCaxCu24O41 (x = 0 and 6) to study the change of the electronic structure near the Fermi level (Ep) by substitution of Sr with Ca. The experimental band structures of both compounds determined by ARPES show a dispersive band near EF, which has a minimum binding energy at ka = (2n+1)π/2 (n=0, ±1, ±2...) with the periodicity of a ladder sublattice. This result indicates that the electronic states near EF originate in the ladder and form aMott-Hubbard band with an energy gap at ka= (2n+1)π/2. This suggests that Cu atoms in the ladder take essentially a divalent state (Cu2+) and "self-doped" holes reside on the chain. It was also found that the dispersive band of Sr8Ca6Cu24O41 is closer to EF than that of Sr14Cu24O41, indicating that the ladder band is "doped" with holes by Ca-substitution. This suggests that the superconductivity observed in a heavily Ca-substituted sample occurs on the ladder.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering