It is generally believed that high-temperature superconductivity occurs in the planes, which is shown in Figure 6.4 .
Many analytical methods work well in three dimensions, but fail in two dimensions.
The Copper-Oxygen Plane, Where the Superconductivity Is Generally Believed to Occur. The arrows denote the quantum spins. At , undergoes a structural transition. The curve is the fit shown in Figure 6.11 . These methods are essentially based on a expansion.