F. Walther Meissner and Robert Ochsenfeld observed in 1933 that a magnetic field was excluded when the metals were cooled below a superconducting critical temperature. John Bardeen, Leon Cooper, and J. Robert Schrieffer won the Nobel Prize for their 1956 paper that explained these effects as the quantum behavior of interacting electrons in a vibrating lattice structure. All of the high-temperature superconductors discovered so far involve strongly correlated electron systems in crystal lattices of copper oxides, or cuprates. Copper atoms are shown in red, oxygen atoms in blue, barium atoms in green, and yttrium in purple.
Superconductivity occurs in the shaded horizontal planes.
Scientists have general notions of how these compounds achieve superconductivity, but the devil is in the details. A two-leg ladder forms a discontinuity in the pattern. Scalapino at UC Santa Barbara has been a pioneer in superconductor research. As a result, they suggested that weakly coupled arrays of such metal-oxide ladders doped with holes could become superconducting. Depending on the doping and the interaction between the ladders, they noted that another result could be a pinned charge density wave of paired holes.