BCS theory of nodal superconductors

TL;DR

This paper reviews the application of BCS theory to various unconventional superconductors and introduces the Volovik quasiclassical approximation to analyze their vortex state thermodynamics and gap symmetry.

Contribution

It extends the Volovik quasiclassical method to describe thermodynamics and thermal conductivity in the vortex state of nodal superconductors.

Findings

Successful application of BCS theory to new superconductor classes

Extension of Volovik's approximation to nodal superconductors

Identification of energy gap symmetry using the extended method

Abstract

This course has a dual purpose. First we review the successes of the weak-coupling BCS theory in describing new classes of superconductors discovered since 1979. They include the heavy-fermion superconductors, high-Tc cuprate superconductors, organic superconductors, Sr2RuO4, etc. Second, we present the quasiclassical approximation introduced by Volovik, which we extend to describe the thermodynamics and the thermal conductivity of the vortex state in nodal superconductors. This approach provides the most powerful tool to identify the symmetry of the energy gap function Delta(k) in these new superconductors.