Hole Doping of the Cu${\mathrm{O}}_2$ Chains in (La,Sr,Ca${)}_{14}$C${\mathrm{u}}_{24}$${\mathrm{O}}_{41}$

Substantial hole doping has been achieved in (La,Sr,Ca${)}_{14}$C${\mathrm{u}}_{24}$ ${\mathrm{O}}_{41}$ compounds with Cu${\mathrm{O}}_2$ chain and C${\mathrm{u}}_2$ ${\mathrm{O}}_3$ ladder building blocks. Holes enter the structural units with larger O/Cu ratios which are the Cu${\mathrm{O}}_2$ 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 Cu${\mathrm{O}}_2$ unit and decreases the resistivity. At the maximum hole concentration $(\sim 0.6/{\mathrm{CuO}}_2)$ the residual moments form a singlet ground state possibly due to dimerization with an excitation gap of $\sim 140\mathrm{K}$ to the triplet state.