Quantum spin liquid theory predicts that doping the spin-ladder material could transform it into a high-Tc superconductor (Philip W. Anderson).
Doping the ladder with holes destroys the spin singlets. Doping with one hole breaks three AF bonds, giving rise to an energy loss proportional to 3J. When two holes are introduced and move independently of each other, the total energy loss is 6J.
The holes tend to share the same rung forming hole bound-states in order to minimize the energy damage. The existence of superconductivity in the doped spin ladder system was theoretically predicted by Dagotto et al. Experimentally superconductivity was first found by Uehara et al, who discovered superconductivity at high pressure in the doped polycrystalline spin ladder compound Sr0.4Ca13.6Cu24O41. Spin ladders demonstrate duperconductivity without phonons: holes bind into pairs.