Current research trends in high temperature superconductivity theory

Abstract

Theoretical interests in high temperature superconductivity started with the pioneering work of Mueller and Bednorz in 1986 on the synthesis of a complicated compound of four ceramic elements (La-Ba-Cu-O) and the subsequent detection of the appearance of superconductivity at a relatively lofty temperature of 35K. Paul Chu and collaborators raised the critical temperature to around 95K by working on another ceramic compound this time from copper, oxygen, barium, and the little known rare earth element yttrium. Hundreds and hundreds of experimental physicists all over the world have been racing to reach higher critical temperatures. In fact, in these cuprate superconductors the transition temperature so far has risen to approximately 134K. It is a well-known experimental fact that the undoped state of cuprates is an insulating antiferromagnet below the Néel temperature, and as additional holes are added to the copper oxide layer, the antiferromagnetic property is suppressed. Eventually, the cuprate system becomes metallic and superconducting. It is widely believed that the spin fluctuations play a key role in determining the physical properties of high-temperature superconductors.
The theoretical explanations of the remarkable properties of these superconductors remain divergent. Several mechanisms have been proposed. Guided by the pairing mechanism of the low-temperature BCS theory, the same basic idea crops up in looking for a possible mechanism for high-temperature superconductors. In this paper we tackle possible mechanisms of high temperature superconductivity including spin-charge separation theory, spin-polaron theory, and anyon superconductivity among others.