Tuning order in cuprate superconductors

In 1986, superconductivity—the ability to transport electrical current without significant resistance—was discovered in cuprate compounds. These materials have fascinated physicists ever since, in part because of the high critical temperatures (Tc’s) below which superconductivity is present and the consequent promise of technological applications. However, cuprate superconductivity also raises fundamental questions about the collective quantum properties of electrons that are confined to a lattice and interact with each other (the “correlated electrons” problem). Hoffman et al. (1) have recently reported an innovative scanning tunnelling microscopy (STM) study which should help answer some of these questions. All discussion of the cuprates begins with the compound La2CuO4. Its valence electrons reside on certain 3d orbitals on the Cu ions which are arranged in layers. In each layer, the Cu