Hole Doping of the CuO₂ Chains in (La, Sr, Ca)₁₄Cu₂₄O₄₁

Substantial hole doping has been achieved in (La, Sr, Ca)₁₄Cu₂₄O₄₁ compounds with CuO₂ chain and Cu₂O₃ ladder building blocks. Holes enter the structural units with larger O/Cu ratios which are the CuO₂ chains. The ladders remain undoped and magnetically inert due to a large spin gap. The moments in the undoped chains interact weakly, and every hole added creates a nonmagnetic CuO₂ unit and decreases the resistivity. At the maximum hole concentration [Formula presented] the residual moments form a singlet ground state possibly due to dimerization with an excitation gap of 140 K to the triplet state.