In the 20 years since the discovery of high-temperature superconductivity in a class of copper-oxide materials, the search for the mechanism underlying this phenomenon has extended beyond the superconducting region itself. Before they are doped to become superconductors, the cuprates are antiferromagnetic insulators, as shown in the phase diagram of figure 1. Researchers have wondered how the material transitions to a robust superconductor as dopants are added and what type of state is reached when the material is overdoped.
A useful way to characterize the electronic states in the underdoped and overdoped regions surrounding the superconducting dome (yellow region in figure 1) is to map out their Fermi surfaces. As the boundary in momentum, or reciprocal (k), space between filled and empty energy levels, the Fermi surface is a key determinant of a material’s physical behavior, such as the temperature dependence of the material’s electrical resistivity....
