Variational cluster approach to s-wave pairing in heavy-fermion superconductors

TL;DR

This paper investigates s-wave Cooper pairing in heavy-fermion systems using the variational cluster approach, revealing coexistence with antiferromagnetism and the importance of interorbital $c$-$f$ pairing.

Contribution

It demonstrates the emergence of s-wave superconductivity coexisting with antiferromagnetism and highlights the critical role of interorbital $c$-$f$ pairing in heavy-fermion models.

Findings

Superconductivity coexists with antiferromagnetism at half filling.

Doping suppresses antiferromagnetism, leading to pure s-wave superconductivity.

Interorbital $c$-$f$ pairing is essential for s-wave superconductivity.

Abstract

We study s-wave Cooper pairing in heavy-fermion systems. We analyze the periodic Anderson model by means of the variational cluster approach (VCA) focusing on the interorbital Cooper pairing between a conduction electron ($c$ electron) and an $f$ electron, called the "$c$-$f$ pairing." It is shown that the s-wave superconductivity appears coexisting with long-range antiferromagnetic order when electrons or holes are doped into the system at half filling. The antiferromagnetic order vanishes when the doping concentration exceeds a certain critical value, leading to a pure s-wave superconducting state. Moreover, the comparative study with different reference systems used in the VCA shows that the interorbital $c$-$f$ pairing is essential for the appearance of the s-wave superconductivity.