Aspects of two-dimensionality in the cuprates

Among the various bulk 3D materials that have a strongly layered structure, the cuprates stand out both as being among the most “2-dimensional” (see below) and as possessing the most interesting phase diagram. The general structure and composition of the cuprates was briefly reviewed in lecture 2: here we concentrate on the phase diagram, just recalling that the basic structure consists of n CuO2 planes per unit cell, spaced relative to one another at ∼ 3.1 Å by “spacer” atoms such as Ca or Y and separated from the next multilayer (next unit cell) by a “charge reservoir” layer that may be up to ∼ 10 Å thick.