Hybrid s-wave superconductivity in CrB$_2$

TL;DR

CrB₂ exhibits a hybrid s-wave superconductivity resulting from the interplay of conventional electron-phonon coupling and unconventional spin fluctuation mechanisms, especially near its antiferromagnetic phase.

Contribution

This study reveals that CrB₂ is a hybrid s-wave superconductor where both conventional and unconventional pairing mechanisms coexist and influence its superconducting properties.

Findings

Superconductivity in CrB₂ is pressure-dependent, with a transition from conventional to hybrid s-wave pairing.

Spin fluctuations significantly contribute to superconductivity near the antiferromagnetic dome.

CrB₂ exemplifies a material where multiple pairing mechanisms combine to produce superconductivity.

Abstract

In a metal with multiple Fermi pockets, the formation of s-wave superconductivity can be conventional due to electron-phonon coupling or unconventional due to spin fluctuations. We analyze the hexagonal diboride CrB$_2$, which is an itinerant antiferromagnet at ambient conditions and turns superconducting upon increasing pressure. While the high pressure behavior of T$_c$ suggests conventional s-wave pairing, we find that spin fluctuations promoting unconventional s-wave pairing become important in the vicinity of the antiferromagnetic dome. As the symmetry class of the s-wave state is independent of its underlying mechanism, we argue that CrB$_2$ is a realization of a hybrid s-wave superconductor where unconventional and conventional s-wave mechanisms team up to form a joint superconducting dome.