FAST TRACK COMMUNICATION: Quantum oscillations in antiferromagnetic CaFe2As2 on the brink of superconductivity

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 alkaline earth AFe₂As₂ antiferromagnets (with A = Ca, Sr and Ba), the dependences of the Fermi surface cross-sectional area F_α and the effective mass m_α^* of the primary observed pocket on the antiferromagnetic/structural transition temperature T_s are both found to be consistent with the case for quasiparticles in a conventional spin-density wave model. These findings suggest that the recently proposed strain-enhanced superconductivity in these materials occurs within a broadly conventional spin-density wave phase.