t-J ladders and cuprate ladder compounds

The properties of strongly correlated electrons confined to move on coupled chains, or ladders, are reviewed. Theoretical interest focuses on the crossover between one and two dimensions which can be achieved by assembling chains to form ladders. The properties at and near half filling are sensitive to the ladder width - ladders with even and odd numbers of legs belong to different families. Cuprates can be synthesized with weakly coupled ladders as key structural units. The recent discovery of superconductivity under pressure in one such cuprate holds promise but many issues remain to be resolved. (orig.)