Chemistry and high temperature superconductivity

Abstract

Seven distinct families of superconductors with critical temperatures at ambient pressure that equal or surpass the historic 23 K limit for Nb₃Ge have been discovered in the last 25 years. Each family is reviewed briefly and their common chemical features are discussed. High temperature superconductors are distinguished by having a high (≥50%) content of nonmetallic elements and fall into two broad classes. ‘Metal–nonmetal’ superconductors require a specific combination of elements such as Cu–O and Fe–As which give rise to the highest known T_c's, probably through a magnetic pairing mechanism. ‘Nonmetal-bonded’ materials contain covalently bonded nonmetal anion networks and are BCS-like superconductors. Fitting an extreme value function to the distribution of T_c values for the known high-T_c families suggests that the probability of a newly discovered superconductor family having maximum T_c > 100 K is ∼0.1 to 1%, decreasing to ∼0.02 to 0.2% for room temperature superconductivity.