Superconductivity

Electrons in metals can self-organise. The complex interplay between lattice dynamics, electrostatic interaction and band structure brings forth numerous types of electronic order. Because of its spectacular phenomenology, superconductivity has enjoyed a central place among these, since its discovery nearly 100 years ago. This short introduction into one of the largest fields of condensed matter research focuses on the most fundamental experimental signatures of superconductivity – perfect conductivity and perfect diamagnetism – and their explanation. A conventional broken symmetry argument is presented, which introduces a superconducting order parameter in analogy to the case of superfluid 4He, and discusses its microscopic origin in the framework of the BCS model of superconductivity. New materials have brought to light novel forms of superconductivity. Many cases are now known which fall outside the orthodox BCS model, ranging from the high temperature superconductors, to various organic and d- and f- metal compounds. The article presents key concepts from this intense area of research and touches on the equally puzzling behaviour of many of these materials above their superconducting transition temperature.