Quantum oscillations in antiferromagnetic CaFe2As2 on the brink of superconductivity

TL;DR

This study investigates the Fermi surface and quasiparticle properties of CaFe2As2 near the onset of superconductivity, revealing a conventional spin-density wave state that coexists with or precedes superconductivity.

Contribution

It provides experimental evidence of Fermi surface reconstruction and quasiparticle behavior consistent with a spin-density wave in CaFe2As2 and related compounds, near the superconducting transition.

Findings

Fermi surface pockets occupy less than 0.05% of the Brillouin zone.

Fermi surface cross-sectional area and effective mass depend on the antiferromagnetic transition temperature.

Results support a conventional spin-density wave model close to superconductivity.

Abstract

We report quantum oscillation measurements on CaFe2As2 under strong magnetic fields- recently reported to become superconducting under pressures of as little as a kilobar. The largest observed carrier pocket occupies less than 0.05 % of the paramagnetic Brillouin zone volume- consistent with Fermi surface reconstruction caused by antiferromagnetism. On comparing several alkali earth AFe2As2 antiferromagnets (with A=Ca,Sr and Ba), the dependence of both the Fermi surface cross-sectional area F_alpha and the effective mass m*_alpha of the primary observed pocket on the antiferromagnetic/structural transition temperature T_s is found to be consistent with quasiparticles in a conventional spin-density wave model. These findings suggest that a conventional spin-density wave exists within close proximity to superconductivity in this series of compounds, which may have implications for the microscopic origin of unconventional pair formation.