A theory governing these materials calculates their free energy as a function of the parameter psi, and one type of these materials consists of normal cores surrounded by vortices. Described by Ginzburg-Landau theory, these materials are limited by a factor of one over e, their London penetration depth, and the exchange of phonons in these causes electrons to form Cooper pairs. These materials are distinguished as Type I or Type II based on the strength of their critical fields. Substances that 
A theory governing these materials calculates their free energy as a function of the parameter psi, and one type of these materials consists of normal cores surrounded by vortices. Described by Ginzburg-Landau theory, these materials are limited by a factor of one over e, their London penetration depth, and the exchange of phonons in these causes electrons to form Cooper pairs. These materials are distinguished as Type I or Type II based on the strength of their critical fields. Substances that transform into these materials eject a magnetic field in the Meissner effect. For 10 points, name these materials that exhibit zero electrical resistance at low temperatures.
A theory governing these materials calculates their free energy as a function of the parameter psi, and one type of these materials consists of normal cores surrounded by vortices.
superconductors [do not prompt on or accept "conductors"]