Study on Unconventional Superconductivity after the BCS Paradigm

Abstract

The Bardeen-Cooper-Schrieffer (BCS) theoretical picture has successfully explained the phenomenon of superconductivity in many single element and alloy superconductors. It suggests that the superconductivity is established through quantum condensation of vast number of Copper pairs formed by exchanging phonons between two electrons with opposite momentum and spins near the Fermi energy. This interesting paradigm has dominated the field of superconductivity since 1957. Many superconductors discovered in past three decades, such as the cuprates, iron pnictide/charcogenide and heavy Fermion superconductors seem, however, to violate the BCS picture to some extent. Most of these new superconducting systems seem to get rid of the phonons, instead use the antiferromagnetic spin fluctuations as the pairing gluons. In cuprate superconductors, the origin for the pairing may be even more exotic. In this short report, we will summarize part of these progresses and try to guide readers to possibly new schemes of superconductivity after the BCS paradigm.